feat(document-page): auto-open transcription panel when ?task=transcribe is present

On mount, reads the task query param before the comment deep-link handler.
When task=transcribe, opens the transcription panel, scrolls the close button
into view, moves focus to it, then strips the param from the URL via replaceState.

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

frontend/src/routes/documents/[id]/+page.svelte

@@ -362,6 +362,19 @@ onMount(() => {
 		);
 	}
 
+	if (page.url.searchParams.get('task') === 'transcribe') {
+		transcribeMode = true;
+		tick().then(() => {
+			const closeBtn = document.querySelector<HTMLElement>('[data-testid="panel-close"]');
+			closeBtn?.scrollIntoView({
+				behavior: prefersReducedMotion ? 'instant' : 'smooth',
+				block: 'nearest'
+			});
+			closeBtn?.focus({ preventScroll: true });
+			replaceState(page.url.pathname, page.state ?? {});
+		});
+	}
+
 	scrollToCommentFromQuery(new URL(page.url), {
 		transcribeMode,
 		setTranscribeMode: (v) => (transcribeMode = v),