Add backend unit test framework and modularize settings UI

Introduced a Vitest-based backend unit testing framework with supporting scripts, helpers, and GitHub Actions integration. Refactored the admin settings page to a modular architecture, splitting monolithic logic into feature-specific tabs and hooks for improved maintainability and testability. Updated documentation to reflect the new testing setup and settings architecture, and added new dependencies for testing utilities.

tests/api/admin-users.routes.test.ts

@@ -0,0 +1,104 @@
+/**
+ * Component: Admin Users API Route Tests
+ * Documentation: documentation/testing.md
+ */
+
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+import { createPrismaMock } from '../helpers/prisma';
+
+let authRequest: any;
+
+const prismaMock = createPrismaMock();
+const requireAuthMock = vi.hoisted(() => vi.fn());
+const requireAdminMock = vi.hoisted(() => vi.fn());
+
+vi.mock('@/lib/db', () => ({
+  prisma: prismaMock,
+}));
+
+vi.mock('@/lib/middleware/auth', () => ({
+  requireAuth: requireAuthMock,
+  requireAdmin: requireAdminMock,
+}));
+
+describe('Admin users routes', () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    authRequest = { user: { sub: 'admin-1', role: 'admin' }, json: vi.fn() };
+    requireAuthMock.mockImplementation((_req: any, handler: any) => handler(authRequest));
+    requireAdminMock.mockImplementation((_req: any, handler: any) => handler());
+  });
+
+  it('returns users list', async () => {
+    prismaMock.user.findMany.mockResolvedValueOnce([{ id: 'u1' }]);
+
+    const { GET } = await import('@/app/api/admin/users/route');
+    const response = await GET({} as any);
+    const payload = await response.json();
+
+    expect(payload.users).toHaveLength(1);
+  });
+
+  it('returns pending users list', async () => {
+    prismaMock.user.findMany.mockResolvedValueOnce([{ id: 'u2' }]);
+
+    const { GET } = await import('@/app/api/admin/users/pending/route');
+    const response = await GET({} as any);
+    const payload = await response.json();
+
+    expect(payload.users).toHaveLength(1);
+  });
+
+  it('updates a user role', async () => {
+    prismaMock.user.findUnique.mockResolvedValueOnce({
+      isSetupAdmin: false,
+      authProvider: 'local',
+      plexUsername: 'user',
+      deletedAt: null,
+    });
+    prismaMock.user.update.mockResolvedValueOnce({ id: 'u3', plexUsername: 'user', role: 'admin' });
+    const request = { json: vi.fn().mockResolvedValue({ role: 'admin' }) };
+
+    const { PUT } = await import('@/app/api/admin/users/[id]/route');
+    const response = await PUT(request as any, { params: Promise.resolve({ id: 'u3' }) });
+    const payload = await response.json();
+
+    expect(payload.user.role).toBe('admin');
+  });
+
+  it('soft deletes a local user', async () => {
+    prismaMock.user.findUnique.mockResolvedValueOnce({
+      id: 'u4',
+      plexUsername: 'user',
+      isSetupAdmin: false,
+      authProvider: 'local',
+      deletedAt: null,
+      _count: { requests: 1 },
+    });
+    prismaMock.user.update.mockResolvedValueOnce({});
+
+    const { DELETE } = await import('@/app/api/admin/users/[id]/route');
+    const response = await DELETE({} as any, { params: Promise.resolve({ id: 'u4' }) });
+    const payload = await response.json();
+
+    expect(payload.success).toBe(true);
+  });
+
+  it('approves a pending user', async () => {
+    prismaMock.user.findUnique.mockResolvedValueOnce({
+      id: 'u5',
+      plexUsername: 'user',
+      registrationStatus: 'pending_approval',
+    });
+    prismaMock.user.update.mockResolvedValueOnce({});
+    const request = { json: vi.fn().mockResolvedValue({ approve: true }) };
+
+    const { POST } = await import('@/app/api/admin/users/[id]/approve/route');
+    const response = await POST(request as any, { params: Promise.resolve({ id: 'u5' }) });
+    const payload = await response.json();
+
+    expect(payload.success).toBe(true);
+  });
+});
+
+