- Use synchronous pool removal in desktop disconnect_db to prevent
race condition when user quickly disconnects and reconnects
- Rename recordMetadataLoadError to recordConnectionLostError and
export it for cross-store reuse
- Sync query execution errors back to connection state via
recordConnectionLostError in queryStore catch blocks
- Add backend check_connection_health method (dbx-core) with Tauri
command and web route for proactive pool verification
- Add frontend checkConnectionHealth API (tauri.ts/http.ts/api.ts)
- Enhance ensureConnected to verify backend pool health before
assuming connection is valid, auto-reconnect if stale