Feat: Make the agent dialog window exposed to the outside world fill in the begin form #3221 (#9124)

### What problem does this PR solve?
Feat: Make the agent dialog window exposed to the outside world fill in
the begin form #3221

### Type of change


- [x] New Feature (non-breaking change which adds functionality)

web/src/components/message-input/next.tsx

@@ -143,6 +143,7 @@ export function NextMessageInput({
                 size="icon"
                 variant="ghost"
                 className="size-7 rounded-sm"
+                disabled={isUploading || sendLoading}
               >
                 <Paperclip className="size-3.5" />
                 <span className="sr-only">Attach file</span>