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/api/tts/edge/route.ts

@@ -77,14 +77,19 @@ export async function POST(request: NextRequest) {
     const { response, boundaries } = await tts.createWithBoundaries(payload);
     const arrayBuffer = await response.arrayBuffer();
 
-    return new NextResponse(arrayBuffer, {
-      status: 200,
-      headers: {
-        'Content-Type': 'audio/mpeg',
-        'Content-Length': arrayBuffer.byteLength.toString(),
-        [WORD_BOUNDARIES_HEADER]: serializeWordBoundaries(boundaries),
-      },
-    });
+    const headers: Record<string, string> = {
+      'Content-Type': 'audio/mpeg',
+      'Content-Length': arrayBuffer.byteLength.toString(),
+    };
+    // Only emit the word-boundary header when it fits well under common
+    // header-size caps (~8KB). Oversized values can be dropped by proxies and
+    // break delivery; the client falls back to [] when the header is absent.
+    const serializedBoundaries = serializeWordBoundaries(boundaries);
+    if (serializedBoundaries.length <= 8192) {
+      headers[WORD_BOUNDARIES_HEADER] = serializedBoundaries;
+    }
+
+    return new NextResponse(arrayBuffer, { status: 200, headers });
   } catch (error) {
     console.error('Edge TTS API error:', error);
     return NextResponse.json(