Module listener 

File watcher and DB pollers for detecting iMessage changes.

Architecture:

1. notify crate watches chat.db + chat.db-wal for fs events
2. 500ms debounce collapses rapid writes into a single poll
3. MessagePoller queries for new/updated messages since last check
4. ChatUpdatePoller queries for read-status changes
5. Events are emitted via a tokio broadcast channel

Structs

IMessageListener

The iMessage listener watches for file system changes and polls the database.