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/dashboard.py

@@ -12,7 +12,7 @@ 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 app.modules.analytics.schemas import (
     AdminDashboardResponse,
     ImportStatsResponse,
@@ -32,7 +32,7 @@ logger = logging.getLogger(__name__)
 @router.get("", response_model=AdminDashboardResponse)
 def get_admin_dashboard(
     db: Session = Depends(get_db),
-    current_admin: User = Depends(get_current_admin_api),
+    current_admin: UserContext = Depends(get_current_admin_api),
 ):
     """Get admin dashboard with platform statistics (Admin only)."""
     user_stats = stats_service.get_user_statistics(db)
@@ -62,7 +62,7 @@ def get_admin_dashboard(
 @router.get("/stats", response_model=StatsResponse)
 def get_comprehensive_stats(
     db: Session = Depends(get_db),
-    current_admin: User = Depends(get_current_admin_api),
+    current_admin: UserContext = Depends(get_current_admin_api),
 ):
     """Get comprehensive platform statistics (Admin only)."""
     stats_data = stats_service.get_comprehensive_stats(db=db)
@@ -81,7 +81,7 @@ def get_comprehensive_stats(
 @router.get("/stats/marketplace", response_model=list[MarketplaceStatsResponse])
 def get_marketplace_stats(
     db: Session = Depends(get_db),
-    current_admin: User = Depends(get_current_admin_api),
+    current_admin: UserContext = Depends(get_current_admin_api),
 ):
     """Get statistics broken down by marketplace (Admin only)."""
     marketplace_stats = stats_service.get_marketplace_breakdown_stats(db=db)
@@ -100,7 +100,7 @@ def get_marketplace_stats(
 @router.get("/stats/platform", response_model=PlatformStatsResponse)
 def get_platform_statistics(
     db: Session = Depends(get_db),
-    current_admin: User = Depends(get_current_admin_api),
+    current_admin: UserContext = Depends(get_current_admin_api),
 ):
     """Get comprehensive platform statistics (Admin only)."""
     user_stats = stats_service.get_user_statistics(db)