Add polling fallback for iMessage listener

[franklinho]

Summary

Adds a periodic polling fallback to the iMessage database listener while keeping the existing fs.watch path for low-latency delivery.

The listener already had a db_poll_interval config default, but the active listener path only reacted to filesystem change events for chat.db / chat.db-wal. On macOS, those events can be missed or delayed even when Messages has committed new rows. When that happens, BlueBubbles does not emit new-message and no FCM notification is sent until a client later runs an incremental sync.

What changed

• Adds pollIntervalMs and a timer to IMessageListener.
• Reuses the existing debounced handleChangeEvent path so watcher events and interval polls share the same lock, lookback, cache trimming, and duplicate-event protection.
• Clears the interval and stops the watcher in stop().
• Wires the interval to existing db_poll_interval config.

Local verification

Reproduced on macOS with an Android BlueBubbles client:

1. A self-message appeared in ~/Library/Messages/chat.db, but the server did not log New Message or send FCM until the Android app later queried /api/v1/message/query.
2. After this patch and repacking the local app, a new self-message produced:
   • server log: New Message from +*******9008, "Hello"
   • server log: [FCMService] Sending FCM notification (Priority: high) to 1 device(s)
   • Android log: Received event of type new-message from Socket.io
   • Android log: Received new message of type new-message from FCM
   • Android active notification on com.bluebubbles.new_messages with tag com.bluebubbles.messaging.NEW_MESSAGE_NOTIFICATION.

Build verification:

cd packages/server
npm run build

This completed successfully.

[zlshames]

can you make the PR for the development branch