fix(notification): remove role=link from view-all button — restores semantically honest button role

The role=link override on a <button> creates a WCAG 4.1.2 keyboard-contract
mismatch: ARIA role=link tells AT users "press Enter to activate (Space does
nothing)", but the native <button> responds to both Enter and Space. Removes
the override so the element is announced as "button" (accurate).

Test selectors updated from getByRole('link') to getByRole('button')
accordingly.

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

frontend/src/lib/notification/NotificationDropdown.svelte

@@ -135,7 +135,6 @@ function handleViewAll() {
 	<div class="border-t border-line px-4 py-2">
 		<button
 			type="button"
-			role="link"
 			onclick={handleViewAll}
 			class="min-h-[44px] px-1 text-xs font-medium text-ink-2 transition-colors hover:text-ink"
 		>

frontend/src/lib/notification/NotificationDropdown.svelte.test.ts

@@ -159,7 +159,7 @@ describe('NotificationDropdown', () => {
 		expect(onMarkAllRead).toHaveBeenCalledOnce();
 	});
 
-	it('calls onClose when the view-all link is clicked', async () => {
+	it('calls onClose when the view-all button is clicked', async () => {
 		const onClose = vi.fn();
 		render(NotificationDropdown, {
 			props: {
@@ -170,12 +170,12 @@ describe('NotificationDropdown', () => {
 			}
 		});
 
-		await page.getByRole('link', { name: /alle aktivitäten|view all/i }).click();
+		await page.getByRole('button', { name: /alle aktivitäten|view all/i }).click();
 
 		expect(onClose).toHaveBeenCalledOnce();
 	});
 
-	it('navigates to /aktivitaeten when the view-all link is clicked', async () => {
+	it('navigates to /aktivitaeten when the view-all button is clicked', async () => {
 		render(NotificationDropdown, {
 			props: {
 				notifications: [],
@@ -185,7 +185,7 @@ describe('NotificationDropdown', () => {
 			}
 		});
 
-		await page.getByRole('link', { name: /alle aktivitäten|view all/i }).click();
+		await page.getByRole('button', { name: /alle aktivitäten|view all/i }).click();
 
 		expect(goto).toHaveBeenCalledWith('/aktivitaeten');
 	});
@@ -203,7 +203,7 @@ describe('NotificationDropdown', () => {
 			}
 		});
 
-		await page.getByRole('link', { name: /alle aktivitäten|view all/i }).click();
+		await page.getByRole('button', { name: /alle aktivitäten|view all/i }).click();
 
 		expect(callOrder).toEqual(['close', 'goto']);
 	});