Step 7.1: player plumbing (PSRAM ring -> AES67 TX), test tone mode

- main/audio_ring: SPSC ring of interleaved int32 frames in PSRAM
  (4 s at 48 kHz stereo), lock-free with acquire/release counters; the
  TX pull callback never blocks.
- main/player: source selection from source.mode and the pull callback
  for aes67_tx. tone -> the core's PTP-phased 1 kHz tone; off -> silence;
  hls/spotify -> ring with 1 s prefill (silence while buffering is not an
  underrun; running dry is, and prefills again). Status fields
  active_source, source_state, spotify_state, buffer_ms. source config
  applies live.
- New source.mode "tone" (validation, UI dropdown, doc) for commissioning.
- Temporary 440 Hz producer in hls mode (until the HLS player exists).
- Verified: tone 999.7 Hz -18 dBFS; off silent; hls 440.0 Hz with max
  sample step 60816 (ideal sine 60825, i.e. no discontinuities), buffer
  3983 ms, 0 underruns; spotify silent/not implemented.

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

main/project_cfg.c

@@ -3,6 +3,7 @@
 
 #include "aes67_cfg.h"
 #include "esp_err.h"
+#include "player.h"
 
 static const char SOURCE_DEFAULTS[] =
     "{\"mode\":\"spotify\",\"spotify_name\":\"P4 AES67\",\"spotify_bitrate\":320,\"hls_url\":\"\","
@@ -10,7 +11,7 @@ static const char SOURCE_DEFAULTS[] =
 
 static bool source_validate(const cJSON *g, char *err, size_t n)
 {
-    static const char *const modes[] = { "spotify", "hls", "auto", "off", NULL };
+    static const char *const modes[] = { "spotify", "hls", "auto", "tone", "off", NULL };
     static const double bitrates[] = { 96, 160, 320 };
     return cfg_check_enum(g, "mode", modes, err, n) &&
            cfg_check_str(g, "spotify_name", 1, 63, err, n) &&
@@ -29,5 +30,5 @@ void project_cfg_defaults(void)
 
 void project_cfg_register(void)
 {
-    ESP_ERROR_CHECK(cfg_register("source", SOURCE_DEFAULTS, source_validate, NULL));
+    ESP_ERROR_CHECK(cfg_register("source", SOURCE_DEFAULTS, source_validate, player_apply));
 }