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/vendor/notifications.py

@@ -14,7 +14,7 @@ from sqlalchemy.orm import Session
 from app.api.deps import get_current_vendor_api
 from app.core.database import get_db
 from app.services.vendor_service import vendor_service
-from models.database.user import User
+from models.schema.auth import UserContext
 from app.modules.messaging.schemas import (
     MessageResponse,
     NotificationListResponse,
@@ -35,7 +35,7 @@ def get_notifications(
     skip: int = Query(0, ge=0),
     limit: int = Query(50, ge=1, le=100),
     unread_only: bool | None = Query(False),
-    current_user: User = Depends(get_current_vendor_api),
+    current_user: UserContext = Depends(get_current_vendor_api),
     db: Session = Depends(get_db),
 ):
     """
@@ -58,7 +58,7 @@ def get_notifications(
 
 @router.get("/unread-count", response_model=UnreadCountResponse)
 def get_unread_count(
-    current_user: User = Depends(get_current_vendor_api),
+    current_user: UserContext = Depends(get_current_vendor_api),
     db: Session = Depends(get_db),
 ):
     """
@@ -75,7 +75,7 @@ def get_unread_count(
 @router.put("/{notification_id}/read", response_model=MessageResponse)
 def mark_as_read(
     notification_id: int,
-    current_user: User = Depends(get_current_vendor_api),
+    current_user: UserContext = Depends(get_current_vendor_api),
     db: Session = Depends(get_db),
 ):
     """
@@ -91,7 +91,7 @@ def mark_as_read(
 
 @router.put("/mark-all-read", response_model=MessageResponse)
 def mark_all_as_read(
-    current_user: User = Depends(get_current_vendor_api),
+    current_user: UserContext = Depends(get_current_vendor_api),
     db: Session = Depends(get_db),
 ):
     """
@@ -108,7 +108,7 @@ def mark_all_as_read(
 @router.delete("/{notification_id}", response_model=MessageResponse)
 def delete_notification(
     notification_id: int,
-    current_user: User = Depends(get_current_vendor_api),
+    current_user: UserContext = Depends(get_current_vendor_api),
     db: Session = Depends(get_db),
 ):
     """
@@ -124,7 +124,7 @@ def delete_notification(
 
 @router.get("/settings", response_model=NotificationSettingsResponse)
 def get_notification_settings(
-    current_user: User = Depends(get_current_vendor_api),
+    current_user: UserContext = Depends(get_current_vendor_api),
     db: Session = Depends(get_db),
 ):
     """
@@ -147,7 +147,7 @@ def get_notification_settings(
 @router.put("/settings", response_model=MessageResponse)
 def update_notification_settings(
     settings: NotificationSettingsUpdate,
-    current_user: User = Depends(get_current_vendor_api),
+    current_user: UserContext = Depends(get_current_vendor_api),
     db: Session = Depends(get_db),
 ):
     """
@@ -164,7 +164,7 @@ def update_notification_settings(
 
 @router.get("/templates", response_model=NotificationTemplateListResponse)
 def get_notification_templates(
-    current_user: User = Depends(get_current_vendor_api),
+    current_user: UserContext = Depends(get_current_vendor_api),
     db: Session = Depends(get_db),
 ):
     """
@@ -185,7 +185,7 @@ def get_notification_templates(
 def update_notification_template(
     template_id: int,
     template_data: NotificationTemplateUpdate,
-    current_user: User = Depends(get_current_vendor_api),
+    current_user: UserContext = Depends(get_current_vendor_api),
     db: Session = Depends(get_db),
 ):
     """
@@ -204,7 +204,7 @@ def update_notification_template(
 @router.post("/test", response_model=MessageResponse)
 def send_test_notification(
     notification_data: TestNotificationRequest,
-    current_user: User = Depends(get_current_vendor_api),
+    current_user: UserContext = Depends(get_current_vendor_api),
     db: Session = Depends(get_db),
 ):
     """