fix(forms): validate JSON tabs before applying or saving

InboundFormModal: switching out of the Advanced tab now parses the three
JSON textareas and rebuilds the structured Inbound via Inbound.fromJson,
so the Basic tab reflects what was pasted. Invalid JSON keeps the user
on Advanced with a specific parse error.

XrayPage: Save now parses xraySetting upfront and snaps the user back to
the Advanced tab on invalid JSON instead of letting the backend reject a
generic blob.

frontend/src/pages/xray/XrayPage.vue

@@ -186,9 +186,6 @@ function onRemoveRoutingRules({ prefix }) {
   );
 }
 
-// `message` is used by some of the in-progress UX flows (kept around
-// because future provisioning errors will surface through it).
-void message;
 const { isMobile } = useMediaQuery();
 
 const basePath = window.X_UI_BASE_PATH || '';
@@ -230,6 +227,17 @@ function onTabChange(key) {
   }
 }
 
+function onSaveAll() {
+  try {
+    JSON.parse(xraySetting.value);
+  } catch (e) {
+    message.error(`Advanced JSON: ${e.message}`);
+    activeTabKey.value = 'tpl-advanced';
+    return;
+  }
+  saveAll();
+}
+
 function syncTabFromHash() {
   const key = keyBySlug[window.location.hash.slice(1)];
   if (key) activeTabKey.value = key;
@@ -268,7 +276,7 @@ onBeforeUnmount(() => {
                     <a-row class="header-row">
                       <a-col :xs="24" :sm="14" class="header-actions">
                         <a-space direction="horizontal">
-                          <a-button type="primary" :disabled="saveDisabled" @click="saveAll">
+                          <a-button type="primary" :disabled="saveDisabled" @click="onSaveAll">
                             {{ t('pages.xray.save') }}
                           </a-button>
                           <a-button type="primary" danger :disabled="!saveDisabled" @click="confirmRestart">