Restructures frontend to a feature-based folder layout

Groups auth, setup, invitation, profile, users, cms, availability and
system code (services/hooks, components, schemas, mocks, pages) under
src/features/<name> instead of splitting by technical layer (api/,
components/, lib/schemas/, mocks/, pages/). Renames the old
connection-oriented `api` layer to `services` per feature, and splits
the monolithic api/types.ts into per-feature types.ts files (with
ProblemDetails/ApiResult merged into lib/api-client.ts as shared
infra). Layout-agnostic code (ui primitives, app shell, i18n, test
utils, lib) stays at the top level.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/features/invitation/pages/InviteCompletePage.test.tsx

@@ -0,0 +1,86 @@
+import { beforeEach, describe, expect, it } from 'vitest';
+import { screen } from '@testing-library/react';
+import userEvent from '@testing-library/user-event';
+import { renderApp, mockGuest } from '@/test/utils';
+import { server } from '@/mocks/server';
+import { setupUninitializedHandlers } from '@/mocks/index';
+import { _resetSetupStatusCache } from '@/router';
+
+// Reset module-level setup status cache before each test.
+beforeEach(() => {
+    _resetSetupStatusCache();
+});
+
+describe('InviteCompletePage', () => {
+    it('shows a loading spinner on mount while validating the token', async () => {
+        server.use(...setupUninitializedHandlers);
+        mockGuest();
+        renderApp('/invite/complete?token=valid-token');
+
+        // Loading spinner should appear immediately.
+        expect(await screen.findByTestId('invite-loading')).toBeInTheDocument();
+    });
+
+    it('shows an error state for an expired token', async () => {
+        server.use(...setupUninitializedHandlers);
+        mockGuest();
+        renderApp('/invite/complete?token=expired-token');
+
+        expect(await screen.findByTestId('invite-error')).toBeInTheDocument();
+        expect(screen.queryByTestId('invite-name-input')).not.toBeInTheDocument();
+    });
+
+    it('shows an error state for a used token', async () => {
+        server.use(...setupUninitializedHandlers);
+        mockGuest();
+        renderApp('/invite/complete?token=used-token');
+
+        expect(await screen.findByTestId('invite-error')).toBeInTheDocument();
+    });
+
+    it('shows an error state when no token is provided', async () => {
+        server.use(...setupUninitializedHandlers);
+        mockGuest();
+        renderApp('/invite/complete');
+
+        expect(await screen.findByTestId('invite-error')).toBeInTheDocument();
+    });
+
+    it('shows the form with a read-only email for a valid token', async () => {
+        server.use(...setupUninitializedHandlers);
+        mockGuest();
+        renderApp('/invite/complete?token=valid-token');
+
+        expect(await screen.findByTestId('invite-name-input')).toBeInTheDocument();
+        const emailInput = screen.getByTestId('invite-email-input') as HTMLInputElement;
+        expect(emailInput.value).toBe('invited@example.com');
+        expect(emailInput.disabled).toBe(true);
+    });
+
+    it('shows validation errors when submitting an empty form', async () => {
+        server.use(...setupUninitializedHandlers);
+        mockGuest();
+        const user = userEvent.setup();
+        renderApp('/invite/complete?token=valid-token');
+
+        const submit = await screen.findByTestId('invite-submit-button');
+        await user.click(submit);
+
+        expect(await screen.findByTestId('invite-name-error')).toBeInTheDocument();
+        expect(screen.getByTestId('invite-password-error')).toBeInTheDocument();
+    });
+
+    it('shows success message after a valid submission', async () => {
+        server.use(...setupUninitializedHandlers);
+        mockGuest();
+        const user = userEvent.setup();
+        renderApp('/invite/complete?token=valid-token');
+
+        await user.type(await screen.findByTestId('invite-name-input'), 'Bob User');
+        await user.type(screen.getByTestId('invite-password-input'), 'ValidPass1!');
+        await user.type(screen.getByTestId('invite-confirmPassword-input'), 'ValidPass1!');
+        await user.click(screen.getByTestId('invite-submit-button'));
+
+        expect(await screen.findByTestId('invite-success')).toBeInTheDocument();
+    });
+});