feat: Add bulletin board system

- Add BoardCategory and BoardPost models with multi-language support
- Add bulletin API endpoints (CRUD, notice toggle, pin toggle)
- Add board_enabled setting to control menu visibility
- Create frontend board pages (list, detail, write, edit)
- Create admin board management and category management pages
- Update Header.tsx with conditional Board menu between Inquiry and Contact Us
- Update admin settings with board_enabled toggle
- Add Board menu to admin sidebar

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

backend/app/schemas/bulletin.py

@@ -0,0 +1,125 @@
+"""
+Bulletin Board Schemas - 게시판 스키마
+"""
+from datetime import datetime
+from typing import Optional, List
+from pydantic import BaseModel
+
+
+# ============ Category Schemas ============
+
+class BoardCategoryBase(BaseModel):
+    name: str
+    name_en: Optional[str] = None
+    name_mn: Optional[str] = None
+    name_ru: Optional[str] = None
+    slug: str
+    description: Optional[str] = None
+    sort_order: int = 0
+    is_active: bool = True
+
+
+class BoardCategoryCreate(BoardCategoryBase):
+    pass
+
+
+class BoardCategoryUpdate(BaseModel):
+    name: Optional[str] = None
+    name_en: Optional[str] = None
+    name_mn: Optional[str] = None
+    name_ru: Optional[str] = None
+    slug: Optional[str] = None
+    description: Optional[str] = None
+    sort_order: Optional[int] = None
+    is_active: Optional[bool] = None
+
+
+class BoardCategoryResponse(BoardCategoryBase):
+    id: int
+    created_at: datetime
+    updated_at: Optional[datetime] = None
+    post_count: int = 0
+
+    class Config:
+        from_attributes = True
+
+
+# ============ Post Schemas ============
+
+class BoardPostBase(BaseModel):
+    title: str
+    content: str
+    category_id: int
+
+
+class BoardPostCreate(BoardPostBase):
+    is_notice: bool = False  # 관리자만 true 가능
+
+
+class BoardPostUpdate(BaseModel):
+    title: Optional[str] = None
+    content: Optional[str] = None
+    category_id: Optional[int] = None
+    is_notice: Optional[bool] = None
+    is_pinned: Optional[bool] = None
+    is_published: Optional[bool] = None
+
+
+class AuthorResponse(BaseModel):
+    id: int
+    name: Optional[str] = None
+    email: str
+    is_admin: bool = False
+
+    class Config:
+        from_attributes = True
+
+
+class BoardPostResponse(BaseModel):
+    id: int
+    title: str
+    content: str
+    category_id: int
+    category: Optional[BoardCategoryResponse] = None
+    author_id: int
+    author: Optional[AuthorResponse] = None
+    is_notice: bool
+    is_pinned: bool
+    is_published: bool
+    view_count: int
+    created_at: datetime
+    updated_at: Optional[datetime] = None
+
+    class Config:
+        from_attributes = True
+
+
+class BoardPostListItem(BaseModel):
+    """목록에서 보여줄 간략한 정보"""
+    id: int
+    title: str
+    category_id: int
+    category_name: Optional[str] = None
+    author_id: int
+    author_name: Optional[str] = None
+    is_notice: bool
+    is_pinned: bool
+    view_count: int
+    created_at: datetime
+
+    class Config:
+        from_attributes = True
+
+
+class BoardPostListResponse(BaseModel):
+    posts: List[BoardPostListItem]
+    notices: List[BoardPostListItem]  # 공지사항 (상단 고정)
+    total: int
+    page: int
+    page_size: int
+    total_pages: int
+
+
+class BoardCategoryListResponse(BaseModel):
+    categories: List[BoardCategoryResponse]
+    total: int