Add SNS Marketing Campaign feature

- Add cash_cc_balance to User model (withdrawable CC)
- Create SnsShareSubmission model for SNS share verification
- Add marketing campaign settings to SystemSettings
- Add reward_type to ReferralReward model
- Create /api/sns-share endpoints for submission and verification
- Add referral signup reward logic (10CC on signup)
- Create /sns-share user page for SNS sharing
- Create /admin/sns-shares management page
- Add marketing settings UI to admin settings page
- Add SNS Shares menu to admin sidebar

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

backend/app/schemas/sns_share.py

@@ -0,0 +1,57 @@
+from pydantic import BaseModel, HttpUrl
+from typing import Optional, List
+from datetime import datetime
+
+
+class SnsShareSubmit(BaseModel):
+    """SNS 공유 제출 요청"""
+    car_id: int
+    platform: str  # twitter, instagram, facebook
+    sns_url: str  # 공유 게시물 URL
+
+
+class SnsShareResponse(BaseModel):
+    """SNS 공유 제출 응답"""
+    id: int
+    user_id: int
+    car_id: int
+    platform: str
+    sns_url: str
+    status: str
+    rejected_reason: Optional[str] = None
+    reward_cc: float
+    rewarded_at: Optional[datetime] = None
+    submitted_at: datetime
+    verified_at: Optional[datetime] = None
+    verified_by: Optional[int] = None
+
+    # Car info for display
+    car_name: Optional[str] = None
+    car_image: Optional[str] = None
+
+    class Config:
+        from_attributes = True
+
+
+class SnsShareListResponse(BaseModel):
+    """SNS 공유 목록 응답"""
+    submissions: List[SnsShareResponse]
+    total: int
+    pending_count: int
+    approved_count: int
+    rejected_count: int
+
+
+class SnsShareVerify(BaseModel):
+    """관리자 검증 요청"""
+    approved: bool
+    rejected_reason: Optional[str] = None
+
+
+class SnsShareStats(BaseModel):
+    """SNS 공유 통계"""
+    total_submissions: int
+    pending_submissions: int
+    approved_submissions: int
+    rejected_submissions: int
+    total_rewarded_cc: float