Add SaaS frontend code (#5879)

# Description of Changes
Adds the code for the SaaS frontend as proprietary code to the OSS repo.
This version of the code is adapted from 22/1/2026, which was the last
SaaS version based on the 'V2' design. This will move us closer to being
able to have the OSS products understand whether the user has a SaaS
account, and provide the correct UI in those cases.

frontend/src/saas/setupTests.ts

@@ -0,0 +1,175 @@
+import '@testing-library/jest-dom';
+import { vi } from 'vitest';
+
+// Mock localStorage for tests
+const localStorageMock = (() => {
+  let store: Record<string, string> = {};
+  return {
+    getItem: vi.fn((key: string) => store[key] || null),
+    setItem: vi.fn((key: string, value: string) => { store[key] = value; }),
+    removeItem: vi.fn((key: string) => { delete store[key]; }),
+    clear: vi.fn(() => { store = {}; }),
+    get length() { return Object.keys(store).length; },
+    key: vi.fn((index: number) => Object.keys(store)[index] || null),
+  };
+})();
+Object.defineProperty(global, 'localStorage', { value: localStorageMock });
+
+// Mock Supabase for tests
+vi.mock('@app/auth/supabase', () => ({
+  supabase: {
+    auth: {
+      getSession: vi.fn().mockResolvedValue({ data: { session: null }, error: null }),
+      refreshSession: vi.fn().mockResolvedValue({ data: { session: null }, error: null }),
+      onAuthStateChange: vi.fn().mockReturnValue({ data: { subscription: { unsubscribe: vi.fn() } } })
+    }
+  },
+  debugAuthEvents: vi.fn()
+}))
+
+// Mock i18next for tests
+vi.mock('react-i18next', () => ({
+  useTranslation: () => ({
+    t: (key: string) => key,
+    i18n: {
+      changeLanguage: vi.fn(),
+    },
+  }),
+  initReactI18next: {
+    type: '3rdParty',
+    init: vi.fn(),
+  },
+  I18nextProvider: ({ children }: { children: React.ReactNode }) => children,
+}));
+
+// Mock i18next-http-backend
+vi.mock('i18next-http-backend', () => ({
+  default: {
+    type: 'backend',
+    init: vi.fn(),
+    read: vi.fn(),
+    save: vi.fn(),
+  },
+}));
+
+// Mock window.URL.createObjectURL and revokeObjectURL for tests
+global.URL.createObjectURL = vi.fn(() => 'mocked-url');
+global.URL.revokeObjectURL = vi.fn();
+
+// Mock File and Blob API methods that aren't available in jsdom
+if (!globalThis.File.prototype.arrayBuffer) {
+  globalThis.File.prototype.arrayBuffer = function() {
+    // Return a simple ArrayBuffer with some mock data
+    const buffer = new ArrayBuffer(8);
+    const view = new Uint8Array(buffer);
+    view.set([1, 2, 3, 4, 5, 6, 7, 8]);
+    return Promise.resolve(buffer);
+  };
+}
+
+if (!globalThis.Blob.prototype.arrayBuffer) {
+  globalThis.Blob.prototype.arrayBuffer = function() {
+    // Return a simple ArrayBuffer with some mock data
+    const buffer = new ArrayBuffer(8);
+    const view = new Uint8Array(buffer);
+    view.set([1, 2, 3, 4, 5, 6, 7, 8]);
+    return Promise.resolve(buffer);
+  };
+}
+
+// Mock crypto.subtle for hashing in tests - force override even if exists
+const mockHashBuffer = new ArrayBuffer(32);
+const mockHashView = new Uint8Array(mockHashBuffer);
+// Fill with predictable mock hash data
+for (let i = 0; i < 32; i++) {
+  mockHashView[i] = i;
+}
+
+// Force override crypto.subtle to avoid Node.js native implementation
+Object.defineProperty(globalThis, 'crypto', {
+  value: {
+    subtle: {
+      digest: vi.fn().mockImplementation(async (_algorithm: string, _data: any) => {
+        // Always return the mock hash buffer regardless of input
+        return mockHashBuffer.slice();
+      }),
+    },
+    getRandomValues: vi.fn().mockImplementation((array: any) => {
+      // Mock getRandomValues if needed
+      for (let i = 0; i < array.length; i++) {
+        array[i] = Math.floor(Math.random() * 256);
+      }
+      return array;
+    }),
+  } as unknown as Crypto,
+  writable: true,
+  configurable: true,
+});
+
+// Mock Worker for tests (Web Workers not available in test environment)
+global.Worker = vi.fn().mockImplementation(() => ({
+  postMessage: vi.fn(),
+  terminate: vi.fn(),
+  addEventListener: vi.fn(),
+  removeEventListener: vi.fn(),
+  onmessage: null,
+  onerror: null,
+}));
+
+// Mock ResizeObserver for Mantine components
+global.ResizeObserver = vi.fn().mockImplementation(() => ({
+  observe: vi.fn(),
+  unobserve: vi.fn(),
+  disconnect: vi.fn(),
+}));
+
+// Mock IntersectionObserver for components that might use it
+global.IntersectionObserver = vi.fn().mockImplementation(() => ({
+  observe: vi.fn(),
+  unobserve: vi.fn(),
+  disconnect: vi.fn(),
+}));
+
+// Mock matchMedia for responsive components
+Object.defineProperty(window, 'matchMedia', {
+  writable: true,
+  value: vi.fn().mockImplementation(query => ({
+    matches: false,
+    media: query,
+    onchange: null,
+    addListener: vi.fn(), // deprecated
+    removeListener: vi.fn(), // deprecated
+    addEventListener: vi.fn(),
+    removeEventListener: vi.fn(),
+    dispatchEvent: vi.fn(),
+  })),
+});
+
+// Mock DOMMatrix for PDF.js tests
+Object.defineProperty(global, 'DOMMatrix', {
+  value: class MockDOMMatrix {
+    a = 1; b = 0; c = 0; d = 1; e = 0; f = 0;
+    m11 = 1; m12 = 0; m13 = 0; m14 = 0;
+    m21 = 0; m22 = 1; m23 = 0; m24 = 0;
+    m31 = 0; m32 = 0; m33 = 1; m34 = 0;
+    m41 = 0; m42 = 0; m43 = 0; m44 = 1;
+    is2D = true;
+    isIdentity = true;
+
+    toString() { return 'matrix(1, 0, 0, 1, 0, 0)'; }
+    scale() { return this; }
+    translate() { return this; }
+    rotate() { return this; }
+    inverse() { return this; }
+    multiply() { return this; }
+
+    static fromFloat32Array() { return new MockDOMMatrix(); }
+    static fromFloat64Array() { return new MockDOMMatrix(); }
+    static fromMatrix() { return new MockDOMMatrix(); }
+  },
+  writable: true,
+  configurable: true,
+})
+
+// Set global test timeout to prevent hangs
+vi.setConfig({ testTimeout: 5000, hookTimeout: 5000 });