feat(calls): rejoin the voice room after a crash, update or reload (#118)

While joined, a device-local record {roomId, deviceId, joinedAt,
lastSeen, mic, video} is written and refreshed every 30 s; a deliberate
hangup (HangupCall/Close) and logout clear it. On the next start, once
the first sync is in and the room's MatrixRTC session has reported its
members (waited for up to 10 s — it fills a moment after sync), a fresh
record (< 10 min) for this device with someone still in the call yields
either a sticky "Rejoin voice?" toast (tap to rejoin) or an automatic
rejoin, per the new Settings → Calls → After a Restart (Ask / Rejoin
automatically / Do nothing; default Ask). Skipped when our own membership
is already live from another device, or only our stale one is left.
Mic/camera state comes from the record (camera still gated by
cameraOnJoin); PTT is applied by startCall as usual.

Pure decision in utils/callRejoin.ts with tests. Verified headless:
reload mid-call → toast → tap → back in the call; hangup → reload → no
toast; auto mode → back in without a prompt.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/state/plaintextCaches.ts

@@ -6,6 +6,7 @@ import { clearRecentGifs } from './recentGifs';
 import { clearRecentStickers } from './recentStickers';
 import { clearNavToActivePathStore } from './navToActivePath';
 import { DRAFT_MSG_KEY_PREFIX } from '../utils/draft';
+import { clearCallSession } from '../utils/callRejoin';
 
 /**
  * [Gitea #41] Wipe every persisted composer draft (`draft-msg-<roomId>`). Drafts
@@ -92,6 +93,7 @@ export const clearPlaintextCaches = (userId?: string): void => {
   clearRecentGifs();
   clearRecentStickers();
   clearMsgDrafts();
+  clearCallSession();
   clearStatusMessage();
   if (userId) clearNavToActivePathStore(userId);
 };