fix: address second round of code review feedback

Backend improvements:
- Create shared validation utility for project name validation
- Add asyncio.Lock to prevent concurrent _query_claude calls
- Fix _create_features_bulk: use flush() for IDs, add rollback on error
- Use unique temp settings file instead of overwriting .claude_settings.json
- Remove exception details from error messages (security)

Frontend improvements:
- Memoize onError callback in ExpandProjectChat for stable dependencies
- Add timeout to start() checkAndSend loop to prevent infinite retries
- Add manuallyDisconnectedRef to prevent reconnection after explicit disconnect
- Clear pending reconnect timeout in disconnect()

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

server/utils/__init__.py

@@ -0,0 +1 @@
+# Server utilities