feat: Add promo preference survey on main page

- Add promo preference fields to User model (promo_preferred_maker,
  promo_preferred_model, promo_email_enabled)
- Create API endpoints for getting/updating promo preferences
- Create PromoPreference component with maker/model selection
- Show login prompt for non-logged-in users when interacting
- Add promo notification service to send emails when matching vehicles
  are added to promotion
- Add multi-language translations (en, mn, ru, ko)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/api/auth.py

@@ -10,6 +10,7 @@ from ..database import get_db
 from ..models import User, SystemSettings, ReferralReward
 from ..models.user import generate_referral_code
 from ..schemas import UserCreate, UserUpdate, UserResponse, Token
+from ..schemas.user import PromoPreferenceUpdate, PromoPreferenceResponse
 from ..config import get_settings
 
 router = APIRouter(prefix="/auth", tags=["auth"])
@@ -277,6 +278,28 @@ def update_me(
     return current_user
 
 
+@router.get("/me/promo-preference", response_model=PromoPreferenceResponse)
+def get_promo_preference(current_user: User = Depends(get_current_user)):
+    """프로모션 선호 차종 조회"""
+    return current_user
+
+
+@router.put("/me/promo-preference", response_model=PromoPreferenceResponse)
+def update_promo_preference(
+    promo_update: PromoPreferenceUpdate,
+    current_user: User = Depends(get_current_user),
+    db: Session = Depends(get_db)
+):
+    """프로모션 선호 차종 설정"""
+    current_user.promo_preferred_maker = promo_update.promo_preferred_maker
+    current_user.promo_preferred_model = promo_update.promo_preferred_model
+    current_user.promo_email_enabled = promo_update.promo_email_enabled
+
+    db.commit()
+    db.refresh(current_user)
+    return current_user
+
+
 # Admin User Management Endpoints
 @router.get("/admin/users")
 def admin_get_users(

backend/app/api/hero_banners.py

@@ -1,4 +1,4 @@
-from fastapi import APIRouter, Depends, HTTPException, UploadFile, File, Query, Body
+from fastapi import APIRouter, Depends, HTTPException, UploadFile, File, Query, Body, BackgroundTasks
 from sqlalchemy.orm import Session
 from typing import List, Optional
 import os
@@ -17,6 +17,7 @@ from ..schemas.hero_banner import (
 from .auth import get_current_user
 from ..models import User
 from ..config import get_settings
+from ..services.promo_notification_service import notify_users_for_promo_vehicle
 
 router = APIRouter(prefix="/hero-banners", tags=["hero-banners"])
 
@@ -309,15 +310,16 @@ async def upload_banner_image(
 # ==================== Banner Toggle & Ordering ====================
 
 @router.post("/admin/toggle/{car_id}")
-def toggle_banner(
+async def toggle_banner(
     car_id: int,
+    background_tasks: BackgroundTasks,
     db: Session = Depends(get_db),
     current_user: User = Depends(get_admin_user)
 ):
     """차량의 배너 상태 토글 (Admin)
 
     - HeroBanner 존재 → 삭제
-    - HeroBanner 없음 → 생성
+    - HeroBanner 없음 → 생성 (+ 프로모션 알림 이메일 전송)
     """
     car = db.query(Car).filter(Car.id == car_id).first()
     if not car:
@@ -360,4 +362,8 @@ def toggle_banner(
         car.is_banner = True
         db.commit()
         db.refresh(banner)
+
+        # Send promo notification emails in background
+        background_tasks.add_task(notify_users_for_promo_vehicle, db, car)
+
         return {"car_id": car_id, "is_banner": True, "banner_id": banner.id, "message": "Added to banner"}

backend/app/models/user.py

@@ -37,6 +37,11 @@ class User(Base):
     phone_verified = Column(Boolean, default=False)
     phone_verified_at = Column(DateTime(timezone=True), nullable=True)
 
+    # Promotion preference (프로모션 선호 차종)
+    promo_preferred_maker = Column(String(100), nullable=True)  # 선호 메이커명
+    promo_preferred_model = Column(String(100), nullable=True)  # 선호 모델명
+    promo_email_enabled = Column(Boolean, default=False)  # 프로모션 이메일 수신 동의
+
     # Account withdrawal/deletion
     withdrawal_requested_at = Column(DateTime(timezone=True), nullable=True)  # 탈퇴 요청 시각
     withdrawal_reason = Column(String(500), nullable=True)  # 탈퇴 사유

backend/app/schemas/user.py

@@ -42,12 +42,31 @@ class UserResponse(BaseModel):
     referral_code: Optional[str] = None  # User's unique referral code
     email_verified: bool = False
     phone_verified: bool = False
+    promo_preferred_maker: Optional[str] = None
+    promo_preferred_model: Optional[str] = None
+    promo_email_enabled: bool = False
     created_at: datetime
 
     class Config:
         from_attributes = True
 
 
+class PromoPreferenceUpdate(BaseModel):
+    """Schema for updating promo preference"""
+    promo_preferred_maker: Optional[str] = None
+    promo_preferred_model: Optional[str] = None
+    promo_email_enabled: bool = False
+
+
+class PromoPreferenceResponse(BaseModel):
+    promo_preferred_maker: Optional[str] = None
+    promo_preferred_model: Optional[str] = None
+    promo_email_enabled: bool = False
+
+    class Config:
+        from_attributes = True
+
+
 class CarViewResponse(BaseModel):
     id: int
     user_id: int

backend/app/services/promo_notification_service.py

@@ -0,0 +1,254 @@
+"""
+Promo Notification Service
+Sends email notifications to users when their preferred vehicle is added to a promotion
+"""
+import smtplib
+from email.mime.text import MIMEText
+from email.mime.multipart import MIMEMultipart
+from typing import List, Optional
+from sqlalchemy.orm import Session
+import asyncio
+
+from ..config import get_settings
+from ..models.user import User
+from ..models.car import Car
+
+settings = get_settings()
+
+
+def get_users_with_matching_preference(
+    db: Session,
+    maker_name: Optional[str] = None,
+    model_name: Optional[str] = None
+) -> List[User]:
+    """
+    Find users whose promo preference matches the given maker/model
+    Only returns users who have promo_email_enabled = True
+    """
+    query = db.query(User).filter(
+        User.promo_email_enabled == True,
+        User.email.isnot(None)
+    )
+
+    if maker_name:
+        # Match maker only (for users who selected maker but any model)
+        # or match exact maker+model
+        query = query.filter(User.promo_preferred_maker == maker_name)
+
+    if model_name:
+        # If model is specified, also filter by model (or users with no model preference)
+        query = query.filter(
+            (User.promo_preferred_model == model_name) |
+            (User.promo_preferred_model.is_(None)) |
+            (User.promo_preferred_model == "")
+        )
+
+    return query.all()
+
+
+async def send_promo_notification_email(
+    email: str,
+    car: Car,
+    language: str = "en"
+) -> bool:
+    """Send promo notification email to a single user"""
+    try:
+        # Email templates by language
+        subjects = {
+            "en": f"AutonetSellCar - Your Preferred Vehicle is Now on Promotion!",
+            "ko": f"AutonetSellCar - 관심 차량이 프로모션에 등록되었습니다!",
+            "mn": f"AutonetSellCar - Таны сонирхсон машин урамшуулалд орлоо!",
+            "ru": f"AutonetSellCar - Ваш желаемый автомобиль теперь в акции!"
+        }
+
+        car_name = car.car_name or "Unknown Vehicle"
+        car_year = car.year or ""
+        car_mileage = f"{car.mileage:,}km" if car.mileage else ""
+        car_url = f"https://autonetsellcar.com/cars/{car.id}"
+
+        bodies = {
+            "en": f"""
+Hello,
+
+Great news! A vehicle matching your preference is now available on promotion!
+
+Vehicle: {car_name}
+Year: {car_year}
+Mileage: {car_mileage}
+
+View this vehicle: {car_url}
+
+As a promoted vehicle, you can view all photos for free!
+
+Best regards,
+AutonetSellCar Team
+
+---
+You received this email because you signed up for promotion notifications.
+To unsubscribe, update your preferences in your account settings.
+""",
+            "ko": f"""
+안녕하세요,
+
+좋은 소식입니다! 관심 차량이 프로모션에 등록되었습니다!
+
+차량: {car_name}
+연식: {car_year}
+주행거리: {car_mileage}
+
+차량 보기: {car_url}
+
+프로모션 차량은 모든 사진을 무료로 보실 수 있습니다!
+
+감사합니다,
+AutonetSellCar 팀
+
+---
+프로모션 알림 신청으로 이 이메일을 받으셨습니다.
+수신 거부를 원하시면 계정 설정에서 변경해 주세요.
+""",
+            "mn": f"""
+Сайн байна уу,
+
+Сайхан мэдээ! Таны сонирхсон машин урамшуулалд орлоо!
+
+Машин: {car_name}
+Он: {car_year}
+Гүйлт: {car_mileage}
+
+Машин үзэх: {car_url}
+
+Урамшуулалтай машины бүх зургийг үнэгүй үзэх боломжтой!
+
+Хүндэтгэсэн,
+AutonetSellCar баг
+
+---
+Та урамшуулалын мэдэгдэл хүлээн авахаар бүртгүүлсэн тул энэ имэйлийг хүлээн авлаа.
+Татгалзахыг хүсвэл данс тохиргооноос өөрчилнө үү.
+""",
+            "ru": f"""
+Здравствуйте,
+
+Отличные новости! Автомобиль, соответствующий вашим предпочтениям, теперь в акции!
+
+Автомобиль: {car_name}
+Год: {car_year}
+Пробег: {car_mileage}
+
+Посмотреть автомобиль: {car_url}
+
+Как акционный автомобиль, вы можете просмотреть все фотографии бесплатно!
+
+С уважением,
+Команда AutonetSellCar
+
+---
+Вы получили это письмо, потому что подписались на уведомления об акциях.
+Чтобы отписаться, измените настройки в вашем аккаунте.
+"""
+        }
+
+        subject = subjects.get(language, subjects["en"])
+        body = bodies.get(language, bodies["en"])
+
+        # Check if SMTP is configured
+        if not settings.SMTP_USER or not settings.SMTP_PASSWORD:
+            # Development mode - just log
+            print(f"[DEV] Promo notification email for {email}: {car_name}")
+            return True
+
+        # Send actual email
+        msg = MIMEMultipart()
+        msg['From'] = f"{settings.SMTP_FROM_NAME} <{settings.SMTP_FROM_EMAIL or settings.SMTP_USER}>"
+        msg['To'] = email
+        msg['Subject'] = subject
+        msg.attach(MIMEText(body, 'plain', 'utf-8'))
+
+        with smtplib.SMTP(settings.SMTP_HOST, settings.SMTP_PORT) as server:
+            server.starttls()
+            server.login(settings.SMTP_USER, settings.SMTP_PASSWORD)
+            server.send_message(msg)
+
+        print(f"[INFO] Promo notification sent to {email} for car {car.id}")
+        return True
+
+    except Exception as e:
+        print(f"[ERROR] Failed to send promo notification to {email}: {e}")
+        return False
+
+
+async def notify_users_for_promo_vehicle(
+    db: Session,
+    car: Car
+) -> int:
+    """
+    Notify all users whose preference matches the car being promoted
+    Returns the number of notifications sent
+    """
+    # Get maker and model names from car
+    maker_name = car.maker.name if car.maker else None
+    model_name = car.model.name if car.model else None
+
+    if not maker_name:
+        print(f"[INFO] Car {car.id} has no maker, skipping promo notifications")
+        return 0
+
+    # Find matching users
+    matching_users = get_users_with_matching_preference(
+        db=db,
+        maker_name=maker_name,
+        model_name=model_name
+    )
+
+    if not matching_users:
+        print(f"[INFO] No users with matching preference for {maker_name} {model_name}")
+        return 0
+
+    print(f"[INFO] Found {len(matching_users)} users with preference for {maker_name} {model_name}")
+
+    # Send notifications
+    sent_count = 0
+    for user in matching_users:
+        if user.email:
+            # Determine language based on user's country
+            language = "en"  # Default
+            if user.country:
+                country_lower = user.country.lower()
+                if country_lower in ["korea", "south korea", "kr", "한국"]:
+                    language = "ko"
+                elif country_lower in ["mongolia", "mn", "монгол"]:
+                    language = "mn"
+                elif country_lower in ["russia", "ru", "россия"]:
+                    language = "ru"
+
+            success = await send_promo_notification_email(
+                email=user.email,
+                car=car,
+                language=language
+            )
+            if success:
+                sent_count += 1
+
+    return sent_count
+
+
+def notify_users_for_promo_vehicle_sync(db: Session, car: Car) -> int:
+    """Synchronous wrapper for notify_users_for_promo_vehicle"""
+    try:
+        loop = asyncio.get_event_loop()
+    except RuntimeError:
+        loop = asyncio.new_event_loop()
+        asyncio.set_event_loop(loop)
+
+    if loop.is_running():
+        # If already in async context, create a task
+        import concurrent.futures
+        with concurrent.futures.ThreadPoolExecutor() as executor:
+            future = executor.submit(
+                asyncio.run,
+                notify_users_for_promo_vehicle(db, car)
+            )
+            return future.result()
+    else:
+        return loop.run_until_complete(notify_users_for_promo_vehicle(db, car))