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/api/api_client.dart

@@ -32,4 +32,8 @@ class ApiClient {
     final response = await _dio.get(path, queryParameters: queryParameters);
     return response.data as Map<String, dynamic>;
   }
+
+  Future<Response> getStream(String path) async {
+    return _dio.get(path, options: Options(responseType: ResponseType.stream));
+  }
 }