refactor: move document transcription, annotation, viewer sub-packages

- transcription/: TranscriptionBlock, Column, EditView, PanelHeader, ReadView,
  Section + transcriptionMarkers, blockConflictMerge, saveBlockWithConflictRetry
  + useBlockAutoSave, useBlockDragDrop hooks
- annotation/: AnnotationLayer, AnnotationShape, AnnotationEditOverlay
- viewer/: PdfViewer, PdfControls + useFileLoader, usePdfRenderer hooks

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

frontend/src/lib/document/viewer/PdfControls.svelte.spec.ts

@@ -0,0 +1,67 @@
+import { vi, describe, it, expect, afterEach } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+import { page } from 'vitest/browser';
+
+import PdfControls from './PdfControls.svelte';
+
+afterEach(cleanup);
+
+const defaultProps = {
+	currentPage: 1,
+	totalPages: 3,
+	isLoaded: true,
+	showAnnotations: false,
+	annotationCount: 0,
+	onPrev: vi.fn(),
+	onNext: vi.fn(),
+	onZoomIn: vi.fn(),
+	onZoomOut: vi.fn(),
+	onToggleAnnotations: vi.fn()
+};
+
+describe('PdfControls — annotation toggle visibility', () => {
+	it('renders annotation toggle when annotationCount is greater than zero', async () => {
+		render(PdfControls, { ...defaultProps, annotationCount: 3 });
+		await expect
+			.element(page.getByRole('button', { name: /annotierungen anzeigen/i }))
+			.toBeInTheDocument();
+	});
+
+	it('does not render annotation toggle when annotationCount is zero', async () => {
+		render(PdfControls, { ...defaultProps, annotationCount: 0 });
+		await expect
+			.element(page.getByRole('button', { name: /annotierungen/i }))
+			.not.toBeInTheDocument();
+	});
+});
+
+describe('PdfControls — annotation toggle label', () => {
+	it('shows "Annotierungen anzeigen" label when annotations are hidden', async () => {
+		render(PdfControls, { ...defaultProps, annotationCount: 2, showAnnotations: false });
+		const btn = page.getByRole('button', { name: /annotierungen anzeigen/i });
+		await expect.element(btn).toBeInTheDocument();
+	});
+
+	it('shows "Annotierungen verbergen" label when annotations are visible', async () => {
+		render(PdfControls, { ...defaultProps, annotationCount: 2, showAnnotations: true });
+		const btn = page.getByRole('button', { name: /annotierungen verbergen/i });
+		await expect.element(btn).toBeInTheDocument();
+	});
+});
+
+describe('PdfControls — annotation toggle contrast (WCAG 2.1 AA)', () => {
+	it('uses text-primary class on annotation toggle button when annotations are hidden', async () => {
+		const { container } = render(PdfControls, {
+			...defaultProps,
+			annotationCount: 2,
+			showAnnotations: false
+		});
+		const allButtons = container.querySelectorAll('button');
+		const annotationBtn = Array.from(allButtons).find((b) =>
+			b.getAttribute('aria-label')?.toLowerCase().includes('annotierungen')
+		);
+		expect(annotationBtn).not.toBeNull();
+		expect(annotationBtn!.className).toContain('text-primary');
+		expect(annotationBtn!.className).not.toContain('text-accent');
+	});
+});