test: comprehensive E2E and API test suite for full KanzlAI stack

Backend (Go):
- Expanded integration_test.go: health, auth middleware (expired/invalid/wrong-secret JWT),
  tenant CRUD, case CRUD (create/list/get/update/delete + filters + validation),
  deadline CRUD (create/list/update/complete/delete), appointment CRUD,
  dashboard (verifies all sections), deadline calculator (valid/invalid/unknown type),
  proceeding types & rules, document endpoints, AI extraction (no-key path),
  and full critical path E2E (auth -> case -> deadline -> appointment -> dashboard -> complete)
- New handler unit tests: case (10), appointment (11), dashboard (1), calculate (5),
  document (10), AI (4) — all testing validation, auth guards, and error paths without DB
- Total: ~80 backend tests (unit + integration)

Frontend (TypeScript/Vitest):
- Installed vitest 2.x, @testing-library/react, @testing-library/jest-dom, jsdom 24, msw
- vitest.config.ts with jsdom env, esbuild JSX automatic, path aliases
- API client tests (13): URL construction, no double /api/, auth header, tenant header,
  POST/PUT/PATCH/DELETE methods, error handling, 204 responses
- DeadlineTrafficLights tests (5): renders cards, correct counts, zero state, onFilter callback
- CaseOverviewGrid tests (4): renders categories, counts, header, zero state
- LoginPage tests (8): form rendering, mode toggle, password login, redirect, error display,
  magic link, registration link
- Total: 30 frontend tests

Makefile: test-frontend target now runs vitest instead of placeholder echo.

frontend/src/__tests__/LoginPage.test.tsx

@@ -0,0 +1,143 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { render, screen, fireEvent, waitFor } from "@testing-library/react";
+
+// Mock next/navigation
+const mockPush = vi.fn();
+const mockRefresh = vi.fn();
+vi.mock("next/navigation", () => ({
+  useRouter: () => ({ push: mockPush, refresh: mockRefresh }),
+}));
+
+// Mock Supabase
+const mockSignInWithPassword = vi.fn();
+const mockSignInWithOtp = vi.fn();
+vi.mock("@/lib/supabase/client", () => ({
+  createClient: () => ({
+    auth: {
+      signInWithPassword: mockSignInWithPassword,
+      signInWithOtp: mockSignInWithOtp,
+    },
+  }),
+}));
+
+// Import after mocks
+const { default: LoginPage } = await import(
+  "@/app/(auth)/login/page"
+);
+
+describe("LoginPage", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it("renders login form with email and password fields", () => {
+    render(<LoginPage />);
+
+    expect(screen.getByText("KanzlAI")).toBeInTheDocument();
+    expect(screen.getByText("Melden Sie sich an")).toBeInTheDocument();
+    expect(screen.getByLabelText("E-Mail")).toBeInTheDocument();
+    expect(screen.getByLabelText("Passwort")).toBeInTheDocument();
+    expect(screen.getByText("Anmelden")).toBeInTheDocument();
+  });
+
+  it("renders mode toggle between Passwort and Magic Link", () => {
+    render(<LoginPage />);
+
+    // "Passwort" appears twice (toggle button + label), so use getAllByText
+    const passwortElements = screen.getAllByText("Passwort");
+    expect(passwortElements.length).toBeGreaterThanOrEqual(1);
+    expect(screen.getByText("Magic Link")).toBeInTheDocument();
+  });
+
+  it("switches to magic link mode and hides password field", () => {
+    render(<LoginPage />);
+
+    fireEvent.click(screen.getByText("Magic Link"));
+
+    expect(screen.queryByLabelText("Passwort")).not.toBeInTheDocument();
+    expect(screen.getByText("Link senden")).toBeInTheDocument();
+  });
+
+  it("submits password login to Supabase", async () => {
+    mockSignInWithPassword.mockResolvedValue({ error: null });
+    render(<LoginPage />);
+
+    fireEvent.change(screen.getByLabelText("E-Mail"), {
+      target: { value: "test@kanzlei.de" },
+    });
+    fireEvent.change(screen.getByLabelText("Passwort"), {
+      target: { value: "geheim123" },
+    });
+    fireEvent.click(screen.getByText("Anmelden"));
+
+    await waitFor(() => {
+      expect(mockSignInWithPassword).toHaveBeenCalledWith({
+        email: "test@kanzlei.de",
+        password: "geheim123",
+      });
+    });
+  });
+
+  it("redirects to / on successful login", async () => {
+    mockSignInWithPassword.mockResolvedValue({ error: null });
+    render(<LoginPage />);
+
+    fireEvent.change(screen.getByLabelText("E-Mail"), {
+      target: { value: "test@kanzlei.de" },
+    });
+    fireEvent.change(screen.getByLabelText("Passwort"), {
+      target: { value: "geheim123" },
+    });
+    fireEvent.click(screen.getByText("Anmelden"));
+
+    await waitFor(() => {
+      expect(mockPush).toHaveBeenCalledWith("/");
+      expect(mockRefresh).toHaveBeenCalled();
+    });
+  });
+
+  it("displays error on failed login", async () => {
+    mockSignInWithPassword.mockResolvedValue({
+      error: { message: "Ungültige Anmeldedaten" },
+    });
+    render(<LoginPage />);
+
+    fireEvent.change(screen.getByLabelText("E-Mail"), {
+      target: { value: "bad@email.de" },
+    });
+    fireEvent.change(screen.getByLabelText("Passwort"), {
+      target: { value: "wrong" },
+    });
+    fireEvent.click(screen.getByText("Anmelden"));
+
+    await waitFor(() => {
+      expect(screen.getByText("Ungültige Anmeldedaten")).toBeInTheDocument();
+    });
+  });
+
+  it("shows magic link sent confirmation", async () => {
+    mockSignInWithOtp.mockResolvedValue({ error: null });
+    render(<LoginPage />);
+
+    // Switch to magic link mode
+    fireEvent.click(screen.getByText("Magic Link"));
+
+    fireEvent.change(screen.getByLabelText("E-Mail"), {
+      target: { value: "test@kanzlei.de" },
+    });
+    fireEvent.click(screen.getByText("Link senden"));
+
+    await waitFor(() => {
+      expect(screen.getByText("Link gesendet")).toBeInTheDocument();
+      expect(screen.getByText("Zurueck zum Login")).toBeInTheDocument();
+    });
+  });
+
+  it("has link to registration page", () => {
+    render(<LoginPage />);
+
+    const registerLink = screen.getByText("Registrieren");
+    expect(registerLink).toBeInTheDocument();
+    expect(registerLink.closest("a")).toHaveAttribute("href", "/register");
+  });
+});