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/.gitignore

@@ -0,0 +1,7 @@
+# Flutter-related
+**/Flutter/ephemeral/
+**/Pods/
+
+# Xcode-related
+**/dgph
+**/xcuserdata/