feat(videocall): integrate videocall feature with architecture refactor

Merges videocall stash, resolves conflicts with installed_apps routes,
and refactors UI to match current legacy patterns:
- Replace themePortProvider with context.sfColors and Theme.of(context)
- Replace showTopSnackbar with feedback dialogs
- Replace hardcoded colors with theme-aware colorScheme
- Wrap test login button in kDebugMode
- Rename error enum values to be more descriptive

packages/navigation/lib/app_routes.dart

@@ -76,6 +76,7 @@ class AppRoutes {
   static const doNotDisturb = '$deviceManagement/do_not_disturb';
   static const callHistory = '$deviceManagement/call_history';
   static const backgroundImage = '$deviceManagement/background_image';
+  static const videocall = '$deviceManagement/videocall';
 
   static const legacyLogin = '$legacy/login';
   static const legacySignup = '$legacy/signup';