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/macos/Flutter/Flutter-Debug.xcconfig

@@ -0,0 +1 @@
+#include "ephemeral/Flutter-Generated.xcconfig"

client_app/macos/Flutter/Flutter-Release.xcconfig

@@ -0,0 +1 @@
+#include "ephemeral/Flutter-Generated.xcconfig"

client_app/macos/Flutter/GeneratedPluginRegistrant.swift

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+//
+//  Generated file. Do not edit.
+//
+
+import FlutterMacOS
+import Foundation
+
+import firebase_auth
+import firebase_core
+import google_sign_in_ios
+import shared_preferences_foundation
+import sign_in_with_apple
+
+func RegisterGeneratedPlugins(registry: FlutterPluginRegistry) {
+  FLTFirebaseAuthPlugin.register(with: registry.registrar(forPlugin: "FLTFirebaseAuthPlugin"))
+  FLTFirebaseCorePlugin.register(with: registry.registrar(forPlugin: "FLTFirebaseCorePlugin"))
+  FLTGoogleSignInPlugin.register(with: registry.registrar(forPlugin: "FLTGoogleSignInPlugin"))
+  SharedPreferencesPlugin.register(with: registry.registrar(forPlugin: "SharedPreferencesPlugin"))
+  SignInWithApplePlugin.register(with: registry.registrar(forPlugin: "SignInWithApplePlugin"))
+}