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/orders.py

@@ -16,7 +16,7 @@ from app.api.deps import get_current_vendor_api
 from app.core.database import get_db
 from app.services.order_inventory_service import order_inventory_service
 from app.services.order_service import order_service
-from models.database.user import User
+from models.schema.auth import UserContext
 from app.modules.orders.schemas import (
     OrderDetailResponse,
     OrderListResponse,
@@ -34,7 +34,7 @@ def get_vendor_orders(
     limit: int = Query(100, ge=1, le=1000),
     status: str | None = Query(None, description="Filter by order status"),
     customer_id: int | None = Query(None, description="Filter by customer"),
-    current_user: User = Depends(get_current_vendor_api),
+    current_user: UserContext = Depends(get_current_vendor_api),
     db: Session = Depends(get_db),
 ):
     """
@@ -67,7 +67,7 @@ def get_vendor_orders(
 @router.get("/{order_id}", response_model=OrderDetailResponse)
 def get_order_details(
     order_id: int,
-    current_user: User = Depends(get_current_vendor_api),
+    current_user: UserContext = Depends(get_current_vendor_api),
     db: Session = Depends(get_db),
 ):
     """
@@ -86,7 +86,7 @@ def get_order_details(
 def update_order_status(
     order_id: int,
     order_update: OrderUpdate,
-    current_user: User = Depends(get_current_vendor_api),
+    current_user: UserContext = Depends(get_current_vendor_api),
     db: Session = Depends(get_db),
 ):
     """
@@ -174,7 +174,7 @@ class ShipmentStatusResponse(BaseModel):
 @router.get("/{order_id}/shipment-status", response_model=ShipmentStatusResponse)
 def get_shipment_status(
     order_id: int,
-    current_user: User = Depends(get_current_vendor_api),
+    current_user: UserContext = Depends(get_current_vendor_api),
     db: Session = Depends(get_db),
 ):
     """
@@ -210,7 +210,7 @@ def ship_order_item(
     order_id: int,
     item_id: int,
     request: ShipItemRequest | None = None,
-    current_user: User = Depends(get_current_vendor_api),
+    current_user: UserContext = Depends(get_current_vendor_api),
     db: Session = Depends(get_db),
 ):
     """