Replace Ring event polling with RingEventListener push stream

[Copilot]

The event detection loop polled ring.active_alerts() every 5 seconds. This is replaced with RingEventListener, which receives push notifications via Firebase Cloud Messaging for real-time event delivery.

Changes

app/database.py

• Added ListenerCredentials table to persist FCM registration credentials across restarts, avoiding re-registration on every startup

app/ring_manager.py

• Replaced the 5-second polling loop in start_listener() with RingEventListener:

  self._event_listener = RingEventListener(
      self.ring,
      credentials,
      self._listener_credentials_updated,
  )
  self._event_listener.add_notification_callback(self._on_event)
  started = await self._event_listener.start()

• Added _on_event(event) callback — resolves device from event.doorbot_id and dispatches capture_video via asyncio.create_task()
• Added DB helpers to load/save FCM credentials; _listener_credentials_updated persists refreshed tokens
• stop() and ring_logout() now call await event_listener.stop()
• _finalise_auth() now awaits start_listener() directly (no longer needs a background task)

app/main.py

• Startup now awaits start_listener() directly instead of wrapping in create_task
• Removed unused asyncio import

Original prompt

Change the event detection from polling to a event stream.

Here is a useful part from the docs

event_listener = RingEventListener(ring, credentials, credentials_updated_callback)
event_listener.add_notification_callback(_event_handler(ring).on_event)
await event_listener.start()

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