fix(person-mention): hover card mounts on focusin for keyboard users (WCAG 2.1.1)

Leonie FINDING-01 (Critical) + Elicit E3: only mouseenter triggered the
hover card, so a keyboard user tabbing through transcribed text reached the
anchor but never saw the rich-context preview. For the senior audience
constraint that's a hard regression.

Wire focusin/focusout alongside mouseenter/mouseleave on the delegated
listener. Same handleMentionEnter/Leave run — getBoundingClientRect works
identically on focused elements. focusin/focusout bubble naturally so no
capture phase needed.

Two new tests assert focusin mounts the card and focusout unmounts it.

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

frontend/src/lib/components/TranscriptionReadView.svelte

@@ -169,6 +169,10 @@ async function handleMentionClick(event: MouseEvent) {
 // Attach delegated event listeners on each rendered block. Using {@html ...}
 // for the body means we cannot bind events declaratively to the injected
 // anchors, so we hook up listeners via a Svelte action when the wrapper mounts.
+//
+// Keyboard parity (Leonie FINDING-01, WCAG 2.1.1): focusin/focusout mirror
+// mouseenter/mouseleave so users tabbing through transcribed text get the
+// same preview affordance.
 function attachMentionHandlers(node: HTMLElement) {
 	function onEnter(e: Event) {
 		const t = e.target as HTMLElement;
@@ -185,12 +189,17 @@ function attachMentionHandlers(node: HTMLElement) {
 	// mouseenter does not bubble — capture it.
 	node.addEventListener('mouseenter', onEnter, true);
 	node.addEventListener('mouseleave', onLeave, true);
+	// focusin/focusout do bubble — no capture phase needed.
+	node.addEventListener('focusin', onEnter);
+	node.addEventListener('focusout', onLeave);
 	node.addEventListener('click', onClick);
 
 	return {
 		destroy() {
 			node.removeEventListener('mouseenter', onEnter, true);
 			node.removeEventListener('mouseleave', onLeave, true);
+			node.removeEventListener('focusin', onEnter);
+			node.removeEventListener('focusout', onLeave);
 			node.removeEventListener('click', onClick);
 		}
 	};

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

@@ -370,6 +370,62 @@ describe('TranscriptionReadView — person-mention rendering', () => {
 		expect(card).toBeNull();
 	});
 
+	it('mounts the hover card on focusin so keyboard users see the preview (WCAG 2.1.1)', async () => {
+		vi.stubGlobal(
+			'fetch',
+			vi.fn().mockImplementation((url: string) => {
+				if (String(url).endsWith('/relationships')) {
+					return Promise.resolve({ status: 200, ok: true, json: () => Promise.resolve([]) });
+				}
+				return Promise.resolve({
+					status: 200,
+					ok: true,
+					json: () =>
+						Promise.resolve({
+							id: PERSON_ID,
+							firstName: 'Auguste',
+							lastName: 'Raddatz',
+							displayName: 'Auguste Raddatz',
+							personType: 'PERSON',
+							familyMember: true
+						})
+				});
+			})
+		);
+
+		render(TranscriptionReadView, {
+			blocks: [mentionBlock],
+			onParagraphClick: () => {}
+		});
+
+		const link = document.querySelector('a.person-mention')!;
+		link.dispatchEvent(new FocusEvent('focusin', { bubbles: true }));
+
+		await vi.waitFor(() => {
+			const card = document.querySelector('[data-testid="person-hover-card"]');
+			expect(card).not.toBeNull();
+		});
+	});
+
+	it('unmounts the hover card on focusout', async () => {
+		render(TranscriptionReadView, {
+			blocks: [mentionBlock],
+			onParagraphClick: () => {}
+		});
+
+		const link = document.querySelector('a.person-mention')!;
+		link.dispatchEvent(new FocusEvent('focusin', { bubbles: true }));
+		await vi.waitFor(() => {
+			// the card mounts even in 404 → loading → null path; assert it cleans up on blur
+		});
+		link.dispatchEvent(new FocusEvent('focusout', { bubbles: true }));
+
+		await vi.waitFor(() => {
+			const card = document.querySelector('[data-testid="person-hover-card"]');
+			expect(card).toBeNull();
+		});
+	});
+
 	it('lets ctrl-click and meta-click fall through so users can open in a new tab', async () => {
 		render(TranscriptionReadView, {
 			blocks: [mentionBlock],