fix: reset relay sockets on visibility change to prevent auth hangs on sleep/wake

When browser tab is hidden (sleep), tear down all relay socket connections
completely. This forces fresh socket creation and clean auth handshake on wake,
preventing stuck AuthStatus.PendingResponse states.

- Add documentVisibility store tracking document.visibilityState
- Call Pool.get().remove(url) for relay sockets during hidden teardown
- Integrate socket reset in syncUserData, syncSpaces, syncDMs
- Add explanatory comments for visibility guards and race conditions

Fixes: App stuck in "Authenticating" after Mac sleep/wake cycle
Tested with: wss://news.utxo.one/

.next/dev/cache/.rscinfo

@@ -0,0 +1 @@
+{"encryption.key":"mT8zxPCClGbcV2DiRln03XdmvHCQ+orzt0Q2KKaiDd4=","encryption.expire_at":1776709211601}