feat: migrate prosapp_web_app from Firebase to NestJS API

- Replace Firebase Auth with JWT stored in SharedPreferences
- Replace Firestore with REST API calls via new ApiService
- Replace Firebase Storage with POST /storage/upload
- Remove firebase_auth, firebase_core, cloud_firestore,
  firebase_storage, firebase_messaging, google_sign_in deps
- Add api_service.dart as central HTTP client

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pubspec.yaml

@@ -38,17 +38,13 @@ dependencies:
   location: ^5.0.3
   flutter_polyline_points: ^2.0.0
   google_maps_flutter: ^2.5.0
-  firebase_auth: ^4.6.2
-  firebase_core: ^2.13.1
   file_picker: ^5.3.2
-  google_sign_in: ^6.1.4  
   provider: ^6.0.5
   package_info_plus: ^4.2.0
   get:
   font_awesome_flutter: ^10.4.0
   flutter_otp_text_field:
   intl_phone_field:
-  cloud_firestore:
   diacritic:
   image_picker: ^1.0.4
   flutter_animate:
@@ -61,12 +57,10 @@ dependencies:
   community_material_icon: ^5.9.55
   flutter_email_sender: ^5.2.0
   webview_flutter: ^4.4.1
-  firebase_storage: ^11.2.2
   responsive_builder: ^0.7.0
   flutter_local_notifications: ^14.1.1
   flutter_dialogs: ^3.0.0
   universal_html: ^2.2.3
-  firebase_messaging: ^14.6.3
   animated_splash_screen: ^1.3.0
   animate_do: ^3.0.2
   shimmer: ^3.0.0