Spotify follows source mode, name and credentials live

- spotify_init() sets up the logger, zeroconf routes and session task
  once; spotify_apply() (at boot and on every source save) enables or
  disables: enabled = mode spotify/auto + credentials. Disable removes
  the mDNS entry, zeroconf answers 404 and a running session ends
  (loop exits within 200 ms, SpircHandler::disconnect stops the queue
  and player tasks). A new device name ends the session and
  re-advertises. The login blob is swapped under a mutex.
- Verified: hls/spotify/rename switch the mDNS entry and /spotify_info
  (404/200) live; switching to hls during Spotify playback ended the
  session in < 2 s, HLS played after ~5 s, internal heap 221 -> 365 KB
  (cspot frees everything).
- CLAUDE.md: OTA-with-session findings (intermittent, flash-write stalls
  seen as TX resyncs during uploads), serial-port reset caveat.

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

CLAUDE.md

@@ -60,10 +60,10 @@ Repo: https://gitea.apointless.space/bsncubed/aes67-ESP32-P4
     - Not yet tested: HE-AAC variant (140k), other stations, fMP4/ADTS-only playlists, discontinuities (#EXT-X-DISCONTINUITY), network loss and recovery, long runs.
     - Audio starts only after PTP lock (~20 s after boot): intended, TX needs PTP.
   - [ ] cspot (Spotify Connect): login, audio, pause/skip/seek and app volume work (7.5b). Open:
-    - OTA during an active Spotify session made the upload crawl (~10 kB/s) and ended in a reset; worked around by pausing Spotify / suspending HLS for the upload (aes67_ota_on_update). Root cause not found (suspect: flash writes stall PSRAM-heavy tasks). Watch for similar stalls.
+    - OTA during an active Spotify session made the upload crawl (~10 kB/s) and ended in a reset. With Spotify paused for the upload (aes67_ota_on_update) 2 of 3 later tries worked, 1 still failed: intermittent, root cause not found. Serial log of a good upload: flash writes stall the TX task > 20 ms about 20x/s (509 'aes67_tx: resync' in 26 s, stream stutters during OTA; none during normal playback). Likely the same stalls hit cspot's network/TLS tasks. Ideas: end the Spotify session (not just pause) for OTA; rate-limit the resync warning.
+    - Opening /dev/ttyACM0 resets the board even with DTR/RTS held low: start serial captures before setting up a test.
     - First connects sometimes fail ("Can't connect to spotify servers"), a retry works.
     - Internal heap drops from ~408 KB to ~232 KB with a session; check what can move to PSRAM.
-    - source.mode changes only start/stop Spotify at boot; in hls mode a running session's audio is dropped (it races through the queue).
     - Mute at 0 % volume not yet confirmed.
   - [ ] failover (auto mode) + /api/player
 - [ ] 8. Mono sum, gain, polish.