feat: close STREAMING.md production readiness gaps

- Added run ID + unique segment naming (r-{ISOTIME}/seg-{seq}.m4s)
- Added fsnotify watcher for real-time R2 segment upload (~7s)
- Added atomic manifest publication (temp key → CopyObject)
- Fixed manifest Cache-Control: public, max-age=1, s-maxage=2, must-revalidate
- Added hls.js error recovery: bounded retries (5x), exponential backoff, reconnecting UI
- Enriched /health endpoint: run_id, active_item, last_segment_seq, last_r2_pub, consecutive_failures, unhealthy detection
- Updated tests: HealthHandler (new fields + unhealthy), player error recovery test
- Updated TODO.md, BACKLOG.md, DONE.md, MEMORY.md

frontend/index.html

@@ -71,6 +71,11 @@
       </section>
     </main>
 
+    <div id="reconnecting-overlay" class="reconnecting-overlay hidden" role="alert" aria-live="assertive">
+      <div class="reconnecting-spinner"></div>
+      <span id="reconnecting-text">Reconnecting...</span>
+    </div>
+
     <script type="module" src="/src/main.ts"></script>
   </body>
 </html>