Phase 2 refinements: Firebase config, dev environment fixes, phase 3 requirement draft

- Integrated Firebase SDK in both Flutter apps (google-services, firebase_options)
- Fixed auth flow, API client, and pairing/status blocs for dev environment
- Added full Flutter project scaffolds (android, ios, web, etc.)
- Added phase 3 chat engine requirement document
- Added bugreport zip pattern to gitignore

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

client_app/lib/core/pairing/pairing_bloc.dart

@@ -77,6 +77,10 @@ class PairingBloc extends Bloc<PairingEvent, PairingState> {
   }
 
   Future<void> _onRequestPairing(RequestPairing event, Emitter<PairingState> emit) async {
+    // Reset to initial so BlocListener can detect new errors
+    if (state is! PairingInitial) {
+      emit(PairingInitial());
+    }
     try {
       final response = await apiClient.post('/api/client/chat/request');
       final data = response['data'] as Map<String, dynamic>;
@@ -104,12 +108,7 @@ class PairingBloc extends Bloc<PairingEvent, PairingState> {
   }
 
   void _listenToSSE(String sessionId) {
-    final dio = Dio(BaseOptions(baseUrl: ApiClient.baseUrl));
-    // SSE endpoint — use responseType stream
-    dio.get(
-      '/api/client/chat/request/$sessionId/status',
-      options: Options(responseType: ResponseType.stream),
-    ).then((response) {
+    apiClient.getStream('/api/client/chat/request/$sessionId/status').then((response) {
       final stream = response.data.stream as Stream<List<int>>;
       _sseSubscription = stream
           .transform(utf8.decoder)