Add typed serial settings operations

Route bounded admin mutations through the existing administration
dispatcher,
covering apply, lifecycle, persistence, authorization, and result
tracking.
Add the browser controls, automatic result refresh, regression coverage,
and
phase documentation.

src/web_serial_settings.h

@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-3.0-only */
+#pragma once
+#include <stdint.h>
+#include "esp_http_server.h"
+
+/* HTTPD owns requests/responses; the existing admin dispatcher alone executes.
+ * One global slot rejects mutations while pending (including execution). GET
+ * exposes only the caller's session result; a later admitted operation replaces
+ * that result, so this is not a durable history or an idempotent retry API.
+ * The 30-second deadline is checked when dequeued, not a completion deadline or
+ * a timer that frees the slot. Revocation/expiry cancels before operation
+ * admission; admitted serial/NVS work may finish after the session is gone. */
+esp_err_t web_serial_settings_handler(httpd_req_t *request);
+void web_serial_settings_execute(uint32_t id);