feat(e2ee): tell the user when their device's key uploads are stuck (#201 KE-1)

When the server keeps rejecting this device's /keys/upload with 400 "One
time key ... already exists", the device's encryption store has diverged
and the SDK retries forever (matrix-rust-sdk#5200, still open). Synapse
saw 474k of these from May 30 to Jul 8 2026. The fix is a fresh login, so:

- keyUploadWatch observes /keys/upload responses through the client's
  fetchFn (the response the SDK gets is untouched; a clone is read).
  Three conflicts within 15 min = stuck; any successful upload clears it.
- KeyUploadBanner (critical strip, same slot as the sync/clock banners):
  "Encryption on this device is out of sync" with Details and
  "Fix: sign out…", which opens the normal logout dialog (it already
  warns when the device isn't verified / backed up).

Server side, Grafana now alerts on the same signal (E2EE Key Upload
Conflicts) and on delayed-event 5xx (Call Delayed-Event Errors).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017PCb59uY3UKqDqt7B6hzd5

src/client/initMatrix.ts

@@ -8,6 +8,7 @@ import { revokeOidcTokens } from './oidcLogout';
 import { pushSessionToSW } from '../sw-session';
 import { deleteSearchCacheDatabase, shouldRunBootCleanup } from '../app/utils/searchCache';
 import { clearPlaintextCaches } from '../app/state/plaintextCaches';
+import { watchKeyUploads } from '../app/utils/keyUploadWatch';
 import { clearSoundboardClipCache } from '../app/utils/soundboardClips';
 import { clearSharedPayload } from '../swShare';
 
@@ -76,6 +77,9 @@ export const initClient = async (session: Session): Promise<MatrixClient> => {
     store: indexedDBStore,
     cryptoStore: legacyCryptoStore,
     deviceId: session.deviceId,
+    // [Gitea #201] Observe /keys/upload so a diverged OTK store is reported to
+    // the user (KeyUploadBanner) instead of retrying silently forever.
+    fetchFn: watchKeyUploads((input, init) => globalThis.fetch(input, init)),
     timelineSupport: true,
     cryptoCallbacks: cryptoCallbacks as any,
     // SAS (emoji) + QR-code verification (show/scan/reciprocate).