feat(notifications): implement /notifications page with filter pills and load-more

New route with server load function (reads URL params, derives unreadCount from
the page, single API call per Sara's architecture requirement), mark-all form
action, and the full page UI: filter pills with ARIA radiogroup, notification
rows with border+dot unread indicators (WCAG 1.4.1), "Ältere laden" client-side
append, and empty state. Includes all de/en/es translation keys.

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

frontend/src/routes/notifications/+page.server.spec.ts

@@ -0,0 +1,136 @@
+import { describe, expect, it, vi, beforeEach } from 'vitest';
+
+vi.mock('$lib/api.server', () => ({ createApiClient: vi.fn() }));
+
+import { load, actions } from './+page.server';
+import { createApiClient } from '$lib/api.server';
+
+beforeEach(() => vi.clearAllMocks());
+
+function makeUrl(params: Record<string, string> = {}) {
+	const url = new URL('http://localhost/notifications');
+	for (const [key, value] of Object.entries(params)) {
+		url.searchParams.set(key, value);
+	}
+	return url;
+}
+
+// ─── load ─────────────────────────────────────────────────────────────────────
+
+describe('notifications page load', () => {
+	it('returns notifications and unreadCount from API response', async () => {
+		const mockGet = vi.fn().mockResolvedValueOnce({
+			response: { ok: true },
+			data: {
+				content: [
+					{ id: 'n1', read: false },
+					{ id: 'n2', read: true },
+					{ id: 'n3', read: false }
+				],
+				totalElements: 3,
+				totalPages: 1,
+				number: 0
+			}
+		});
+		vi.mocked(createApiClient).mockReturnValue({ GET: mockGet } as ReturnType<
+			typeof createApiClient
+		>);
+
+		const result = await load({ url: makeUrl(), fetch: vi.fn() as unknown as typeof fetch });
+
+		expect(result.notifications).toHaveLength(3);
+		expect(result.unreadCount).toBe(2);
+	});
+
+	it('passes type param to API when ?type=MENTION is in URL', async () => {
+		const mockGet = vi.fn().mockResolvedValueOnce({
+			response: { ok: true },
+			data: { content: [], totalElements: 0, totalPages: 0, number: 0 }
+		});
+		vi.mocked(createApiClient).mockReturnValue({ GET: mockGet } as ReturnType<
+			typeof createApiClient
+		>);
+
+		await load({ url: makeUrl({ type: 'MENTION' }), fetch: vi.fn() as unknown as typeof fetch });
+
+		const queryParams = mockGet.mock.calls[0][1].params.query;
+		expect(queryParams.type).toBe('MENTION');
+	});
+
+	it('passes read=false to API when ?read=false is in URL', async () => {
+		const mockGet = vi.fn().mockResolvedValueOnce({
+			response: { ok: true },
+			data: { content: [], totalElements: 0, totalPages: 0, number: 0 }
+		});
+		vi.mocked(createApiClient).mockReturnValue({ GET: mockGet } as ReturnType<
+			typeof createApiClient
+		>);
+
+		await load({ url: makeUrl({ read: 'false' }), fetch: vi.fn() as unknown as typeof fetch });
+
+		const queryParams = mockGet.mock.calls[0][1].params.query;
+		expect(queryParams.read).toBe(false);
+	});
+
+	it('passes no filter params when no search params present', async () => {
+		const mockGet = vi.fn().mockResolvedValueOnce({
+			response: { ok: true },
+			data: { content: [], totalElements: 0, totalPages: 0, number: 0 }
+		});
+		vi.mocked(createApiClient).mockReturnValue({ GET: mockGet } as ReturnType<
+			typeof createApiClient
+		>);
+
+		await load({ url: makeUrl(), fetch: vi.fn() as unknown as typeof fetch });
+
+		const queryParams = mockGet.mock.calls[0][1].params.query;
+		expect(queryParams.type).toBeUndefined();
+		expect(queryParams.read).toBeUndefined();
+	});
+
+	it('calls the API exactly once — no separate round-trip for unreadCount', async () => {
+		const mockGet = vi.fn().mockResolvedValueOnce({
+			response: { ok: true },
+			data: { content: [], totalElements: 0, totalPages: 0, number: 0 }
+		});
+		vi.mocked(createApiClient).mockReturnValue({ GET: mockGet } as ReturnType<
+			typeof createApiClient
+		>);
+
+		await load({ url: makeUrl(), fetch: vi.fn() as unknown as typeof fetch });
+
+		expect(mockGet).toHaveBeenCalledTimes(1);
+	});
+
+	it('throws 401 error when API returns 401', async () => {
+		const mockGet = vi.fn().mockResolvedValueOnce({
+			response: { ok: false, status: 401 },
+			data: null
+		});
+		vi.mocked(createApiClient).mockReturnValue({ GET: mockGet } as ReturnType<
+			typeof createApiClient
+		>);
+
+		await expect(
+			load({ url: makeUrl(), fetch: vi.fn() as unknown as typeof fetch })
+		).rejects.toMatchObject({ status: 401 });
+	});
+});
+
+// ─── mark-all action ──────────────────────────────────────────────────────────
+
+describe('notifications mark-all action', () => {
+	it('calls POST /api/notifications/read-all and redirects', async () => {
+		const mockPost = vi.fn().mockResolvedValueOnce({ response: { ok: true } });
+		vi.mocked(createApiClient).mockReturnValue({ POST: mockPost } as ReturnType<
+			typeof createApiClient
+		>);
+
+		const markAll = actions['mark-all'] as (ctx: { fetch: typeof fetch }) => Promise<never>;
+		await expect(markAll({ fetch: vi.fn() as unknown as typeof fetch })).rejects.toMatchObject({
+			location: '/notifications'
+		});
+
+		expect(mockPost).toHaveBeenCalledTimes(1);
+	});
+});