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/windows/flutter/generated_plugin_registrant.cc

@@ -0,0 +1,17 @@
+//
+//  Generated file. Do not edit.
+//
+
+// clang-format off
+
+#include "generated_plugin_registrant.h"
+
+#include <firebase_auth/firebase_auth_plugin_c_api.h>
+#include <firebase_core/firebase_core_plugin_c_api.h>
+
+void RegisterPlugins(flutter::PluginRegistry* registry) {
+  FirebaseAuthPluginCApiRegisterWithRegistrar(
+      registry->GetRegistrarForPlugin("FirebaseAuthPluginCApi"));
+  FirebaseCorePluginCApiRegisterWithRegistrar(
+      registry->GetRegistrarForPlugin("FirebaseCorePluginCApi"));
+}