Silent error swallowing made it impossible to diagnose why worker
couldn't see master's heartbeat. Now logs errors from:
- updateNodeState upsert failures
- writeStateToSharedMariaDB connection/write failures
- getNodeStatesShared query failures
- list endpoint shows state count in logs
Also improved First() call to not overwrite state on error.
Bump version to v1.6.5.
When master uses SQLite locally, updateNodeState only wrote to local DB.
Workers querying shared MariaDB never saw the master's heartbeat.
Now master also writes its heartbeat to the shared MariaDB via a
temporary connection when MariaDB connection settings are configured.
Bump version to v1.6.4.
