refactor(TranscriptionReadView): remove dead else branch in handleMentionLeave

Only mouseleave is wired in attachMentionHandlers so the else branch
could never fire.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/components/TranscriptionReadView.svelte

@@ -155,11 +155,7 @@ async function handleMentionEnter(event: Event) {
 function handleMentionLeave(event: Event) {
 	const link = event.target as HTMLAnchorElement;
 	link.removeAttribute('aria-describedby');
-	if (event.type === 'mouseleave') {
-		scheduleCardClose();
-	} else {
-		activeCard = null;
-	}
+	scheduleCardClose();
 }
 
 /**