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_cookie_auth.h

@@ -17,3 +17,6 @@ esp_err_t web_cookie_auth_require(httpd_req_t *request, bool mutation,
                                   bool upgrade, web_session_view_t *view,
                                   bool *allowed);
 esp_err_t web_cookie_auth_handler(httpd_req_t *request);
+/* Same mutation policy, allowing a bounded body; caller validates JSON/content type. */
+esp_err_t web_cookie_auth_require_json(httpd_req_t *request, size_t body_limit,
+                                      web_session_view_t *view, bool *allowed);