fix: bot-review robustness fixes (TTS sync, updater, nightly, a11y) (#4659)

Cherry-picked and re-verified the applicable subset of
julianshen/readest@fa1b74a0 (its "address PR #15 bot reviews" commit). The
fork-only AI-annotation-tool change was dropped — readest has no 'ai' toolbar
tool. Each logic fix is covered by a failing-first test.

- TTS position sequence is now an app-wide monotonic counter, so a fresh
  TTSController (constructed per `tts-speak`) isn't dropped by consumers holding
  `lastSequenceSeen` from a prior session.
- share.ts only swallows AbortError (user cancel); other failures — e.g.
  NotAllowedError when a quick action fires without a user gesture — fall back to
  the clipboard so the text still reaches the user.
- document.isTxt tolerates MIME params (text/plain;charset=utf-8), uppercase
  extensions (BOOK.TXT), and a nameless Blob, so a TXT can't slip onto the
  non-text path and yield a null book.
- updater getNightlyPlatformKey matches x86_64/aarch64 explicitly; a 32-bit or
  otherwise unknown arch yields no nightly instead of mis-routing to aarch64.
- UpdaterWindow downloadWithProgress resolves on tauriDownload completion even
  when Content-Length is absent (no more hang on portable/AppImage/Android).
- nightly_update.rs uses async tokio::fs::read in the async command.
- nightly.yml: serialize runs via a concurrency group (no cancel) and
  persist-credentials:false on checkouts.
- edge TTS route only emits the word-boundary header when it fits under ~8KB;
  oversized values get dropped by proxies, and the client falls back to [].
- RSVPOverlay drops the contradictory aria-disabled on the functional rate
  button (it opens the pace picker).
- nightly verify harness handles artifact stream errors instead of crashing.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/readest-app/src/app/reader/components/rsvp/RSVPOverlay.tsx

@@ -760,15 +760,14 @@ const RSVPOverlay: React.FC<RSVPOverlayProps> = ({
 
         {/* WPM selector — while RSVP follows TTS the timer no longer paces, so it
             becomes an "Audio pace" affordance that opens a TTS rate picker
-            instead (decision 6). aria-disabled (not hard-disabled) keeps it
-            focusable as a hint; the lock glyph + border reads in e-ink without
-            relying on opacity. */}
+            instead (decision 6). It stays a real, enabled button (it opens the
+            picker), so no aria-disabled; the lock glyph + border reads in e-ink
+            without relying on opacity. */}
         <div className='relative shrink-0'>
           {ttsDriven ? (
             <button
               className='eink-bordered flex items-center gap-1.5 rounded-full border border-gray-500/20 bg-gray-500/10 px-3 py-1.5 text-sm transition-colors hover:bg-gray-500/20'
               onClick={() => setShowRateDropdown(!showRateDropdown)}
-              aria-disabled='true'
               aria-label={_('Audio pace')}
               title={_('Speed follows audio')}
             >