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/auth-is-local-admin.routes.test.ts

@@ -0,0 +1,47 @@
+/**
+ * Component: Is Local Admin API Route Tests
+ * Documentation: documentation/backend/services/auth.md
+ */
+
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+
+const requireAuthMock = vi.fn();
+const isLocalAdminMock = vi.fn();
+
+vi.mock('@/lib/middleware/auth', () => ({
+  requireAuth: requireAuthMock,
+  isLocalAdmin: isLocalAdminMock,
+}));
+
+describe('Is local admin route', () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+  });
+
+  it('returns false when request has no user', async () => {
+    requireAuthMock.mockImplementation((_req: any, handler: any) => handler({}));
+    const { GET } = await import('@/app/api/auth/is-local-admin/route');
+
+    const response = await GET({} as any);
+    const payload = await response.json();
+
+    expect(response.status).toBe(200);
+    expect(payload.isLocalAdmin).toBe(false);
+    expect(isLocalAdminMock).not.toHaveBeenCalled();
+  });
+
+  it('returns local admin status for user', async () => {
+    requireAuthMock.mockImplementation((_req: any, handler: any) =>
+      handler({ user: { id: 'user-1' } })
+    );
+    isLocalAdminMock.mockResolvedValue(true);
+    const { GET } = await import('@/app/api/auth/is-local-admin/route');
+
+    const response = await GET({} as any);
+    const payload = await response.json();
+
+    expect(response.status).toBe(200);
+    expect(payload.isLocalAdmin).toBe(true);
+    expect(isLocalAdminMock).toHaveBeenCalledWith('user-1');
+  });
+});