feat(transcription): clicking annotation focuses corresponding block

Pass activeAnnotationId to TranscriptionEditView. An $effect watches
it and sets activeBlockId to the block matching the annotation,
activating its turquoise focus border.

2 new tests (RED/GREEN):
- activates block matching activeAnnotationId (turquoise border)
- no block activated when activeAnnotationId is null

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

frontend/src/lib/components/TranscriptionEditView.svelte.spec.ts

@@ -55,6 +55,23 @@ describe('TranscriptionEditView — rendering', () => {
 	});
 });
 
+describe('TranscriptionEditView — annotation sync', () => {
+	it('activates block matching activeAnnotationId', async () => {
+		renderView({ activeAnnotationId: 'a2' });
+		// Block 2 (annotation a2) should have turquoise border
+		const block = document.querySelector('[data-block-id="b2"]')!;
+		expect(block.className).toContain('border-turquoise');
+	});
+
+	it('does not activate any block when activeAnnotationId is null', async () => {
+		renderView({ activeAnnotationId: null });
+		const block1 = document.querySelector('[data-block-id="b1"]')!;
+		const block2 = document.querySelector('[data-block-id="b2"]')!;
+		expect(block1.className).not.toContain('border-turquoise');
+		expect(block2.className).not.toContain('border-turquoise');
+	});
+});
+
 describe('TranscriptionEditView — reorder', () => {
 	it('renders move-up button disabled on first block', async () => {
 		renderView();