New headphones app icon set, hardened streaming and playback, download removal controls

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

README.md

@@ -44,3 +44,23 @@ Tap the ↓ on a book (or "Download" in the player) to save it on the device. Do
 - **To open the app itself offline, serve it over HTTPS.** Browsers only allow the service worker (`sw.js`) on secure
   origins. Put a reverse proxy with a certificate in front of port 8080 (and a domain name). Over plain HTTP, downloads
   still play but the page can't load without a connection.
+
+## Troubleshooting playback
+
+Run this on the player server (or `docker exec -it audiobook-player python server.py check`):
+
+```bash
+python3 server.py check
+```
+
+It logs in to OpenAudible, lists a few books' files, and tests whether each file can stream to a phone. iPhones will
+only play audio from a server that answers byte-range requests; if OpenAudible doesn't, the player server emulates
+them (seeking in very large books is slower). The container's log (`docker logs audiobook-player`) notes when that happens
+and records any upstream errors.
+
+The player also recovers by itself from dropped connections and stalls (it reloads from the same spot, up to four times),
+and your position is saved every few seconds, on pause, and when the page is closed or backgrounded.
+
+## Icons
+
+`python3 tools/make_icons.py` regenerates the app icons (needs Pillow).