feat(annotation): add dimmed prop to AnnotationLayer

Hides block number badges and disables hover/active visual feedback
when dimmed=true. Click handlers remain active for scroll-sync.

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

frontend/src/lib/components/AnnotationLayer.svelte.test.ts

@@ -0,0 +1,67 @@
+import { describe, it, expect } from 'vitest';
+import { render } from 'vitest-browser-svelte';
+import { page } from 'vitest/browser';
+import AnnotationLayer from './AnnotationLayer.svelte';
+import type { Annotation } from '$lib/types';
+
+const annotation: Annotation = {
+	id: 'ann-1',
+	documentId: 'doc-1',
+	pageNumber: 1,
+	x: 0.1,
+	y: 0.2,
+	width: 0.3,
+	height: 0.1,
+	color: '#00c7b1',
+	createdAt: '2026-01-01T00:00:00Z'
+};
+
+describe('AnnotationLayer', () => {
+	describe('dimmed prop', () => {
+		it('should hide block number badges when dimmed is true', async () => {
+			render(AnnotationLayer, {
+				annotations: [annotation],
+				canDraw: false,
+				color: '#00c7b1',
+				blockNumbers: { 'ann-1': 1 },
+				dimmed: true,
+				onDraw: () => {}
+			});
+
+			const badge = page.getByText('1');
+			await expect.element(badge).not.toBeInTheDocument();
+		});
+
+		it('should show block number badges when dimmed is false', async () => {
+			render(AnnotationLayer, {
+				annotations: [annotation],
+				canDraw: false,
+				color: '#00c7b1',
+				blockNumbers: { 'ann-1': 1 },
+				dimmed: false,
+				onDraw: () => {}
+			});
+
+			const badge = page.getByText('1');
+			await expect.element(badge).toBeInTheDocument();
+		});
+
+		it('should still fire onAnnotationClick when dimmed', async () => {
+			let clickedId: string | undefined;
+			render(AnnotationLayer, {
+				annotations: [annotation],
+				canDraw: false,
+				color: '#00c7b1',
+				dimmed: true,
+				onDraw: () => {},
+				onAnnotationClick: (id: string) => {
+					clickedId = id;
+				}
+			});
+
+			const el = document.querySelector('[data-testid="annotation-ann-1"]')!;
+			el.dispatchEvent(new MouseEvent('click', { bubbles: true }));
+			expect(clickedId).toBe('ann-1');
+		});
+	});
+});