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/users.py

@@ -16,7 +16,7 @@ from app.api.deps import get_current_admin_api
 from app.core.database import get_db
 from app.services.admin_service import admin_service
 from app.services.stats_service import stats_service
-from models.database.user import User
+from models.schema.auth import UserContext
 from models.schema.auth import (
     UserCreate,
     UserDeleteResponse,
@@ -40,7 +40,7 @@ def get_all_users(
     role: str = Query("", description="Filter by role"),
     is_active: str = Query("", description="Filter by active status"),
     db: Session = Depends(get_db),
-    current_admin: User = Depends(get_current_admin_api),
+    current_admin: UserContext = Depends(get_current_admin_api),
 ):
     """Get paginated list of all users (Admin only)."""
     # Convert string params to proper types
@@ -70,7 +70,7 @@ def get_all_users(
 def create_user(
     user_data: UserCreate = Body(...),
     db: Session = Depends(get_db),
-    current_admin: User = Depends(get_current_admin_api),
+    current_admin: UserContext = Depends(get_current_admin_api),
 ):
     """Create a new user (Admin only)."""
     user = admin_service.create_user(
@@ -108,7 +108,7 @@ def create_user(
 @router.get("/stats")
 def get_user_statistics(
     db: Session = Depends(get_db),
-    current_admin: User = Depends(get_current_admin_api),
+    current_admin: UserContext = Depends(get_current_admin_api),
 ):
     """Get user statistics for admin dashboard (Admin only)."""
     return stats_service.get_user_statistics(db)
@@ -119,7 +119,7 @@ def search_users(
     q: str = Query(..., min_length=2, description="Search query (username or email)"),
     limit: int = Query(10, ge=1, le=50),
     db: Session = Depends(get_db),
-    current_admin: User = Depends(get_current_admin_api),
+    current_admin: UserContext = Depends(get_current_admin_api),
 ):
     """
     Search users by username or email (Admin only).
@@ -134,7 +134,7 @@ def search_users(
 def get_user_details(
     user_id: int = Path(..., description="User ID"),
     db: Session = Depends(get_db),
-    current_admin: User = Depends(get_current_admin_api),
+    current_admin: UserContext = Depends(get_current_admin_api),
 ):
     """Get detailed user information (Admin only)."""
     user = admin_service.get_user_details(db=db, user_id=user_id)
@@ -164,7 +164,7 @@ def update_user(
     user_id: int = Path(..., description="User ID"),
     user_update: UserUpdate = Body(...),
     db: Session = Depends(get_db),
-    current_admin: User = Depends(get_current_admin_api),
+    current_admin: UserContext = Depends(get_current_admin_api),
 ):
     """Update user information (Admin only)."""
     update_data = user_update.model_dump(exclude_unset=True)
@@ -206,7 +206,7 @@ def update_user(
 def toggle_user_status(
     user_id: int = Path(..., description="User ID"),
     db: Session = Depends(get_db),
-    current_admin: User = Depends(get_current_admin_api),
+    current_admin: UserContext = Depends(get_current_admin_api),
 ):
     """Toggle user active status (Admin only)."""
     user, message = admin_service.toggle_user_status(
@@ -223,7 +223,7 @@ def toggle_user_status(
 def delete_user(
     user_id: int = Path(..., description="User ID"),
     db: Session = Depends(get_db),
-    current_admin: User = Depends(get_current_admin_api),
+    current_admin: UserContext = Depends(get_current_admin_api),
 ):
     """Delete a user (Admin only)."""
     message = admin_service.delete_user(