refactor(api): introduce UserContext schema for API dependency injection

Replace direct User database model imports in API endpoints with UserContext
schema, following the architecture principle that API routes should not import
database models directly.

Changes:
- Create UserContext schema in models/schema/auth.py with from_user() factory
- Update app/api/deps.py to return UserContext from all auth dependencies
- Add _get_user_model() helper for functions needing User model access
- Update 58 API endpoint files to use UserContext instead of User
- Add noqa comments for 4 legitimate edge cases (enums, internal helpers)

Architecture validation: 0 errors (down from 61), 11 warnings remain

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

app/api/v1/admin/platforms.py

@@ -23,7 +23,7 @@ from sqlalchemy.orm import Session
 
 from app.api.deps import get_current_admin_from_cookie_or_header, get_db
 from app.services.platform_service import platform_service
-from models.database.user import User
+from models.schema.auth import UserContext
 
 logger = logging.getLogger(__name__)
 router = APIRouter(prefix="/platforms")
@@ -142,7 +142,7 @@ def _build_platform_response(db: Session, platform) -> PlatformResponse:
 @router.get("", response_model=PlatformListResponse)
 async def list_platforms(
     db: Session = Depends(get_db),
-    current_user: User = Depends(get_current_admin_from_cookie_or_header),
+    current_user: UserContext = Depends(get_current_admin_from_cookie_or_header),
     include_inactive: bool = Query(False, description="Include inactive platforms"),
 ):
     """
@@ -163,7 +163,7 @@ async def list_platforms(
 async def get_platform(
     code: str = Path(..., description="Platform code (oms, loyalty, etc.)"),
     db: Session = Depends(get_db),
-    current_user: User = Depends(get_current_admin_from_cookie_or_header),
+    current_user: UserContext = Depends(get_current_admin_from_cookie_or_header),
 ):
     """
     Get platform details by code.
@@ -179,7 +179,7 @@ async def update_platform(
     update_data: PlatformUpdateRequest,
     code: str = Path(..., description="Platform code"),
     db: Session = Depends(get_db),
-    current_user: User = Depends(get_current_admin_from_cookie_or_header),
+    current_user: UserContext = Depends(get_current_admin_from_cookie_or_header),
 ):
     """
     Update platform settings.
@@ -201,7 +201,7 @@ async def update_platform(
 async def get_platform_stats(
     code: str = Path(..., description="Platform code"),
     db: Session = Depends(get_db),
-    current_user: User = Depends(get_current_admin_from_cookie_or_header),
+    current_user: UserContext = Depends(get_current_admin_from_cookie_or_header),
 ):
     """
     Get detailed statistics for a platform.