Player: auto mode fails over between Spotify and HLS

No Spotify session (or paused, with failover_on_pause) for failover_delay_s
switches to HLS; Spotify playing switches back within ~1 s. Switches fade
out/in over 30 ms and flush the ring. HLS is suspended while Spotify plays.
cspot is held back instead of drained while it isn't Spotify's turn: it keeps
decoding on pause, so dropping its frames let it race through the queue.

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

main/hls.h

@@ -11,5 +11,8 @@
 typedef bool (*hls_sink_t)(const uint8_t *data, size_t len, bool segment_start);
 
 esp_err_t hls_start(hls_sink_t sink);
-// Stop fetching (current download is abandoned) until resumed.
-void hls_suspend(bool suspend);
+// Stop fetching (current download is abandoned) until resumed. Reasons are independent:
+// fetching runs only when no reason holds it.
+#define HLS_SUSPEND_OTA      (1 << 0)
+#define HLS_SUSPEND_FAILOVER (1 << 1)
+void hls_suspend(unsigned reason, bool suspend);