The provider only kept the most recent message in `lastMessage`, so two
messages arriving in the same tick were coalesced and one was lost. Add a
`subscribe(messageType, handler)` registry that delivers every message to
its handlers without coalescing, and move the provider's own `Play` and
`LibraryChanged` handling onto it.
`lastMessage` is kept (now deprecated) for `useWebsockets`, which still
consumes it for GeneralCommand handling.
Handle the server's LibraryChanged WebSocket message to invalidate
library-dependent React Query caches when items are added/updated/
removed, so newly added episodes/movies appear without a manual
refresh. Debounced to coalesce a scan's burst of events.
Add useRefreshLibraryOnFocus as a fallback that re-checks on screen
focus (throttled, online-only, skips first focus), wired into home
(mobile + TV) and the library pages.
Move reconnectAttempts from local variable to useRef so it persists
across recursive connectWebSocket calls. Previously, each call reset
the counter to 0, causing infinite reconnection attempts instead of
stopping at the max of 5.
Also reset the counter on successful connection (onopen) so fresh
reconnection attempts get full retries.
