Fix: Fixed the issue where the thinking mode on the chat page could not be turned off #9789 (#9794)

### What problem does this PR solve?

Fix: Fixed the issue where the thinking mode on the chat page could not
be turned off #9789

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

web/src/pages/next-chats/chat/app-settings/dynamic-variable.tsx

@@ -41,6 +41,11 @@ export function DynamicVariableForm() {
           <Plus />
         </Button>
       </div>
+      <div className="flex gap-2 pr-12 text-text-secondary text-xs">
+        <span className="flex-1">Key</span>
+        <span className="w-3"></span>
+        <span className="flex-1">Optional</span>
+      </div>
       <div className="space-y-5">
         {fields.map((field, index) => {
           const typeField = `${name}.${index}.key`;