docs: add README hardware guide/wiring, sdkconfig.defaults.esp32 Wi-Fi preset, guard placeholder SSID from STA retry loop

main/wifi_manager.c

@@ -85,7 +85,9 @@ esp_err_t wifi_manager_start(void)
     const char *ssid = CONFIG_MTG_WIFI_SSID;
     const char *pass = CONFIG_MTG_WIFI_PASS;
 
-    if (strlen(ssid) == 0) {
+    /* Empty SSID, or an untouched sdkconfig.defaults.esp32 placeholder:
+     * keep station mode disabled so we don't hammer a bogus AP at boot. */
+    if (strlen(ssid) == 0 || strstr(ssid, "YOUR_") != NULL) {
         ESP_LOGW(TAG, "no SSID configured - Wi-Fi station skipped (set CONFIG_MTG_WIFI_SSID)");
         return ESP_OK;
     }