Boot chime through ES8311: audio-out path verified on hardware

C5->E5 half-second chime with fade-out at boot, right after the face
renders. Codec opens in slave mode, esp_codec_dev write path works.
Phase 1 bring-up is now complete: display, touch, audio, 200MHz PSRAM.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

firmware/main/desklock_main.c

@@ -10,12 +10,51 @@
  * Current stage: bring-up — display + a placeholder face.
  */
 
+#include <math.h>
+#include <stdlib.h>
+
 #include "esp_log.h"
 #include "bsp/esp-bsp.h"
+#include "esp_codec_dev.h"
 #include "lvgl.h"
 
 static const char *TAG = "desklock";
 
+#define CHIME_RATE 16000
+#define CHIME_SAMPLES (CHIME_RATE / 2) /* 0.5 s */
+
+/* Bring-up proof for the audio path: C5 -> E5 with a fade-out. */
+static void play_boot_chime(void)
+{
+    esp_codec_dev_handle_t spk = bsp_audio_codec_speaker_init();
+    if (spk == NULL) {
+        ESP_LOGW(TAG, "speaker init failed — no chime");
+        return;
+    }
+    esp_codec_dev_sample_info_t fs = {
+        .sample_rate = CHIME_RATE,
+        .channel = 1,
+        .bits_per_sample = 16,
+    };
+    esp_codec_dev_set_out_vol(spk, 70);
+    esp_codec_dev_open(spk, &fs);
+
+    int16_t *buf = malloc(CHIME_SAMPLES * sizeof(int16_t));
+    if (buf != NULL) {
+        float phase = 0.0f;
+        for (int i = 0; i < CHIME_SAMPLES; i++) {
+            float freq = (i < CHIME_SAMPLES / 2) ? 523.25f : 659.25f;
+            phase += 2.0f * (float)M_PI * freq / CHIME_RATE;
+            float envelope = 1.0f - (float)i / CHIME_SAMPLES;
+            buf[i] = (int16_t)(sinf(phase) * 12000.0f * envelope);
+        }
+        esp_codec_dev_write(spk, buf, CHIME_SAMPLES * sizeof(int16_t));
+        free(buf);
+        ESP_LOGI(TAG, "boot chime played");
+    }
+    esp_codec_dev_close(spk);
+}
+
 static void show_placeholder_face(void)
 {
     bsp_display_lock(0);
@@ -50,6 +89,7 @@ void app_main(void)
     bsp_display_start();
     bsp_display_backlight_on();
     show_placeholder_face();
+    play_boot_chime();
 
     ESP_LOGI(TAG, "DeskLock up (placeholder face)");