fix: fix: transcribe audio before mention check in groups with requireMention (openclaw#9973) thanks @mcinteerj

Verified:
- pnpm install --frozen-lockfile
- pnpm build
- pnpm check
- pnpm test

Co-authored-by: mcinteerj <3613653+mcinteerj@users.noreply.github.com>

src/media-understanding/types.ts

@@ -10,6 +10,7 @@ export type MediaAttachment = {
   url?: string;
   mime?: string;
   index: number;
+  alreadyTranscribed?: boolean;
 };
 
 export type MediaUnderstandingOutput = {