Stability round 2: WIFI_PS_NONE + 10MHz SDIO

1-bit bus alone did not stop the sdio_write timeout wedge (recurred
at ~5min uptime). Modem power save is the new prime suspect: the C6
napping mid-SDIO-transaction matches the minutes-scale periodicity.
Always-powered appliance -> PS_NONE costs ~50mW and removes the
entire failure class if correct. SDIO clock also halved to 10MHz.

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

firmware/main/net.c

@@ -83,6 +83,8 @@ static void wifi_event(void *arg, esp_event_base_t base, int32_t id, void *data)
     } else if (base == IP_EVENT && id == IP_EVENT_STA_GOT_IP) {
         ip_event_got_ip_t *ev = (ip_event_got_ip_t *)data;
         s_got_ip = true;
+        /* always-powered appliance: modem sleep wedges the hosted SDIO link */
+        esp_wifi_set_ps(WIFI_PS_NONE);
         ESP_LOGI(TAG, "got ip " IPSTR, IP2STR(&ev->ip_info.ip));
         setenv("TZ", "CET-1CEST,M3.5.0,M10.5.0/3", 1);
         tzset();

firmware/sdkconfig.defaults

@@ -51,7 +51,7 @@ CONFIG_ESP_HOSTED_DFLT_TASK_FROM_SPIRAM=n
 # hosted 2.x: keep internal RAM for task stacks; buffers go to PSRAM
 CONFIG_ESP_HOSTED_MEMPOOL_PREFER_SPIRAM=y
 # conservative SDIO clock for first data-path proof (raise after verification)
-CONFIG_ESP_HOSTED_SDIO_CLOCK_FREQ_KHZ=20000
+CONFIG_ESP_HOSTED_SDIO_CLOCK_FREQ_KHZ=10000
 
 # headroom for diag event handlers that touch LVGL
 CONFIG_ESP_SYSTEM_EVENT_TASK_STACK_SIZE=4096