fix(middleware): prevent premature redirect to /login during loading

Users were incorrectly redirected to /login during the initial loading phase
before the loading was actually complete. Added loading_started and
loading_complete flags to properly track the initialization state so
the setup redirect middleware knows when it's safe to redirect.

src/server/api/auth.py

@@ -117,6 +117,10 @@ async def setup_auth(req: SetupRequest):
         # Store master password hash in config's other field
         config.other['master_password_hash'] = password_hash
         
+        # Mark that loading has been initiated (used by middleware to prevent
+        # premature redirect to /login after setup)
+        config.other['loading_started'] = True
+        
         # Store anime directory in config's other field if provided
         anime_directory = None
         if req.anime_directory: