Pink noise as a source (mode "pink")

Core: aes67_tx_pink_noise(), a ready-made TX source: xorshift32 white noise
through Paul Kellet's pink filter, -18 dBFS RMS (peaks about -6 dBFS), same
on L and R. The player uses it like the tone (straight to TX, no volume or
gain). Checked on the board: -18 dBFS RMS, octave bands 63 Hz-4 kHz flat
within +-0.4 dB, L = R.

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

main/player.h

@@ -1,4 +1,4 @@
-// Project player: picks the audio source for AES67 TX (test tone, silence, HLS, Spotify).
+// Project player: picks the audio source for AES67 TX (test tone, pink noise, silence, HLS, Spotify).
 #pragma once
 
 #include <stddef.h>
@@ -7,7 +7,7 @@
 #include "cJSON.h"
 #include "esp_err.h"
 
-typedef enum { PLAYER_SRC_TONE, PLAYER_SRC_OFF, PLAYER_SRC_HLS, PLAYER_SRC_SPOTIFY } player_src_t;
+typedef enum { PLAYER_SRC_TONE, PLAYER_SRC_OFF, PLAYER_SRC_HLS, PLAYER_SRC_SPOTIFY, PLAYER_SRC_PINK } player_src_t;
 
 esp_err_t player_init(void);
 // Apply the "source" config group (mode etc.).