Fix touch crash + make rain a reachability signal + calm the alarm churn

TOUCH CRASH (the blue screen): app_on_touch ran a blocking WebSocket
send (up to 5s) directly in the LVGL touch callback, stalling the
MIPI-DSI flush into a garbage/blue frame + task-watchdog reboot on
every tap. Now touch_cb only gives a semaphore; a dedicated app_task
does the blocking sends, audio, and face changes off the render
thread. WS send timeout cut 5s to 1.5s as belt-and-braces.

RAIN = REACHABILITY (user request): rain now falls only while the
gateway WebSocket is live (gated on gw_connected in rain_tick). It
drains gracefully on disconnect, resumes on reconnect, a genuine
glanceable reachable signal. Idle density bumped 2 to 4 so
connected-idle reads distinctly from disconnected-black.

CALM THE WEDGE CHURN (user request): transient wifi/WS drops no longer
slam to the x_x error face or a CONNECTING banner. Boot goes straight
to the calm idle face (dry until connected). Only a sustained 30s+
outage escalates to x_x (clock_cb); the ~15s wedge-recovery just shows
a brief rain pause.

Two fixes from adversarial concurrency review before flashing:
- persistent single capture task (was xTaskCreate per utterance; a
  rapid re-tap or WS-stop-vs-app-start race could put two readers on
  one mic/I2S handle and corrupt the codec)
- reset s_talking on disconnect (app_on_disconnect) so the first tap
  after a mid-utterance drop starts fresh, not the stop branch

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

firmware/main/audio.c

@@ -35,6 +35,7 @@ static volatile bool s_capturing;
 
 typedef enum { JOB_GONG, JOB_REPLY } job_t;
 static QueueHandle_t s_jobs;
+static TaskHandle_t s_capture_task;
 
 /* --- gong: see docs/architecture.md "Sound signature" --- */
 
@@ -126,17 +127,23 @@ static void audio_task(void *arg)
     }
 }
 
+/* One persistent capture task, created once. It parks on a notification until
+ * capture is requested, then streams mic -> gateway while s_capturing holds.
+ * This makes capture single-instance: no create/delete restart race, so a rapid
+ * re-tap (or a WS-disconnect stop racing an app_task start) can never put two
+ * readers on the one mic/I2S handle. */
 static void capture_task(void *arg)
 {
     (void)arg;
     uint8_t *chunk = heap_caps_malloc(CAPTURE_CHUNK, MALLOC_CAP_DEFAULT);
-    while (s_capturing) {
-        if (esp_codec_dev_read(s_mic, chunk, CAPTURE_CHUNK) == ESP_CODEC_DEV_OK) {
-            gw_send_bin(chunk, CAPTURE_CHUNK);
+    for (;;) {
+        ulTaskNotifyTake(pdTRUE, portMAX_DELAY);
+        while (s_capturing) {
+            if (esp_codec_dev_read(s_mic, chunk, CAPTURE_CHUNK) == ESP_CODEC_DEV_OK) {
+                gw_send_bin(chunk, CAPTURE_CHUNK);
+            }
         }
     }
-    free(chunk);
-    vTaskDelete(NULL);
 }
 
 void audio_init(void)
@@ -159,6 +166,7 @@ void audio_init(void)
     s_reply = heap_caps_malloc(REPLY_MAX, MALLOC_CAP_SPIRAM);
     s_jobs = xQueueCreate(4, sizeof(job_t));
     xTaskCreate(audio_task, "audio", 4096, NULL, 5, NULL);
+    xTaskCreate(capture_task, "capture", 4096, NULL, 6, &s_capture_task);
     ESP_LOGI(TAG, "audio up (spk=%d mic=%d)", s_spk != NULL, s_mic != NULL);
 }
 
@@ -170,11 +178,11 @@ void audio_play_gong(void)
 
 void audio_capture_start(void)
 {
-    if (s_mic == NULL || s_capturing) {
+    if (s_mic == NULL || s_capturing || s_capture_task == NULL) {
         return;
     }
     s_capturing = true;
-    xTaskCreate(capture_task, "capture", 4096, NULL, 6, NULL);
+    xTaskNotifyGive(s_capture_task); /* wake the persistent task's inner loop */
 }
 
 void audio_capture_stop(void)