fix(room-nav): expiring timed mute no longer clobbers a manual mode change

unmuteRoom unconditionally reset the room to Unset when a timed mute expired
(in-session timer and boot-time restore alike), silently reverting a mode the
user had changed by hand during the window. Mute-timer helpers move to
muteTimers.ts; unmuteRoom now reads the live push-rule mode and only resets
when it is still Mute, always dropping the persisted timer. Unit-tested.

Fixes #21

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/pages/client/ClientNonUIFeatures.tsx

@@ -51,7 +51,7 @@ import {
   MuteTimerEntry,
   loadMuteTimers,
   unmuteRoom,
-} from '../../features/room-nav/RoomNavItem';
+} from '../../features/room-nav/muteTimers';
 import { STATUS_EXPIRY_KEY, STATUS_MSG_KEY } from '../../features/settings/account/Profile';
 import { useDeepLinkNavigate } from '../../hooks/useDeepLinkNavigate';
 import { toastQueueAtom } from '../../state/toast';