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.server.ts

@@ -35,21 +35,6 @@ export async function load({ fetch, locals }) {
 }
 
 export const actions = {
-	createUser: async ({ request, fetch }) => {
-		const data = await request.formData();
-		const api = createApiClient(fetch);
-
-		const result = await api.POST('/api/users', {
-			body: {
-				username: data.get('username') as string,
-				initialPassword: data.get('password') as string,
-				groupIds: data.getAll('groupIds') as string[]
-			}
-		});
-
-		return toActionResult(result);
-	},
-
 	deleteUser: async ({ request, fetch }) => {
 		const data = await request.formData();
 		const id = data.get('id') as string;