refactor(api): tighten login and wrapper typing (#34447)

api/dify_app.py

@@ -1,5 +1,14 @@
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
 from flask import Flask
 
+if TYPE_CHECKING:
+    from extensions.ext_login import DifyLoginManager
+
 
 class DifyApp(Flask):
-    pass
+    """Flask application type with Dify-specific extension attributes."""
+
+    login_manager: DifyLoginManager