fix(pdf-controls): add focus-visible ring to all PdfControls buttons (WCAG 2.1 §2.4.7)

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

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

@@ -66,6 +66,35 @@ describe('PdfControls — annotation toggle contrast (WCAG 2.1 AA)', () => {
 	});
 });
 
+describe('PdfControls — focus rings (WCAG 2.1 §2.4.7)', () => {
+	it('annotation toggle button has focus-visible:ring-2 focus ring', 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('focus-visible:ring-2');
+	});
+
+	it('icon-only nav/zoom buttons each have focus-visible:ring-2 focus ring', async () => {
+		const { container } = render(PdfControls, { ...defaultProps });
+		const allButtons = container.querySelectorAll('button');
+		const iconOnlyButtons = Array.from(allButtons).filter((b) => {
+			const label = b.getAttribute('aria-label') ?? '';
+			return ['zurück', 'weiter', 'verkleinern', 'vergrößern'].includes(label.toLowerCase());
+		});
+		expect(iconOnlyButtons).toHaveLength(4);
+		for (const btn of iconOnlyButtons) {
+			expect(btn.className).toContain('focus-visible:ring-2');
+		}
+	});
+});
+
 describe('PdfControls — touch targets (WCAG 2.2 §2.5.8)', () => {
 	it('annotation toggle button has min-h-[44px] touch target', async () => {
 		const { container } = render(PdfControls, {