feat: the frontend part of mcp (#22131)

Co-authored-by: jZonG <jzongcode@gmail.com>
Co-authored-by: Novice <novice12185727@gmail.com>
Co-authored-by: nite-knite <nkCoding@gmail.com>
Co-authored-by: Hanqing Zhao <sherry9277@gmail.com>

web/app/components/base/prompt-editor/plugins/placeholder.tsx

@@ -8,7 +8,7 @@ const Placeholder = ({
   className,
 }: {
   compact?: boolean
-  value?: string
+  value?: string | JSX.Element
   className?: string
 }) => {
   const { t } = useTranslation()