feat(admin): add dedicated routes for admin user management (#37)

- New GET /admin/users/new page: create user with all profile fields
  (login, password, firstName, lastName, birthDate, email, contact, groups)
- New GET /admin/users/[id] page: edit user profile, groups, and
  optional password change without requiring current password
- New PUT /api/users/{id} backend endpoint (ADMIN_USER permission)
  with AdminUpdateUserRequest DTO for admin-override user updates
- Refactored admin users tab: replaced inline editing with edit links
  to dedicated routes; create button now links to /admin/users/new
- Extended CreateUserRequest with profile fields so new users can be
  created with full profile data in a single request
- Added 28 component tests across 3 new spec files (TDD)

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

frontend/src/routes/admin/page.svelte.spec.ts

@@ -0,0 +1,80 @@
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+import { page } from 'vitest/browser';
+import Page from './+page.svelte';
+
+vi.mock('$app/forms', () => ({ enhance: () => () => {} }));
+
+const makeGroup = (overrides = {}) => ({
+	id: 'g1',
+	name: 'Editoren',
+	permissions: ['WRITE_ALL'],
+	...overrides
+});
+
+const makeUser = (overrides = {}) => ({
+	id: 'u1',
+	username: 'max',
+	firstName: 'Max',
+	lastName: 'Mustermann',
+	email: 'max@example.com',
+	birthDate: undefined,
+	contact: undefined,
+	enabled: true,
+	groups: [makeGroup()],
+	createdAt: '2024-01-01T00:00:00Z',
+	...overrides
+});
+
+const baseData = {
+	users: [makeUser()],
+	groups: [makeGroup()],
+	tags: []
+};
+
+afterEach(cleanup);
+
+// ─── Users tab ────────────────────────────────────────────────────────────────
+
+describe('Admin page – users tab', () => {
+	it('shows the username in the table', async () => {
+		render(Page, { data: baseData });
+		await expect.element(page.getByRole('cell', { name: 'max', exact: true })).toBeInTheDocument();
+	});
+
+	it('shows the full name in the table', async () => {
+		render(Page, { data: baseData });
+		await expect.element(page.getByText(/Max Mustermann/)).toBeInTheDocument();
+	});
+
+	it('shows a dash when user has no name set', async () => {
+		const data = { ...baseData, users: [makeUser({ firstName: undefined, lastName: undefined })] };
+		render(Page, { data });
+		await expect.element(page.getByText('–')).toBeInTheDocument();
+	});
+
+	it('shows group badges for the user', async () => {
+		render(Page, { data: baseData });
+		await expect.element(page.getByText('Editoren')).toBeInTheDocument();
+	});
+
+	it('edit link points to /admin/users/[id]', async () => {
+		render(Page, { data: baseData });
+		await expect
+			.element(page.getByRole('link', { name: /Bearbeiten/i }))
+			.toHaveAttribute('href', '/admin/users/u1');
+	});
+
+	it('new user button links to /admin/users/new', async () => {
+		render(Page, { data: baseData });
+		await expect
+			.element(page.getByRole('link', { name: /Neuer Benutzer/i }))
+			.toHaveAttribute('href', '/admin/users/new');
+	});
+
+	it('shows "no groups" label when user has no groups', async () => {
+		const data = { ...baseData, users: [makeUser({ groups: [] })] };
+		render(Page, { data });
+		await expect.element(page.getByText(/Keine Gruppen/i)).toBeInTheDocument();
+	});
+});