Scaffold HIPCTF platform (NestJS + Angular)

- Backend: NestJS 10 + TypeORM (better-sqlite3) feature-modular layout.
  - Entities: user, setting, category, challenge, challenge_file, solve,
    refresh_token, blog_post. Auto-run migrations + idempotent 6-system-
    category seed on startup.
  - Argon2id password hashing with policy check; JWT access + rotating
    refresh tokens (HttpOnly cookie); CSRF middleware (SameSite + custom
    X-CSRF-Token header); global JWT auth guard with @Public() opt-out;
    per-IP login backoff + per-IP registration rate limit.
  - Endpoints: auth (login/refresh/logout/csrf), users (first-admin
    registration), system (bootstrap/event status/SSE), admin (guarded
    user CRUD with last-admin invariant), frontend module (uploads +
    SPA fallback).
  - Security: helmet+CSP+HSTS-gated-by-TLS, CORS allowlist, structured
    global exception filter, Zod request validation pipes, OpenAPI 3.1
    served at /api/docs and /api/docs-json, 10 canonical themes under
    backend/themes/.
- Frontend: Angular 17 standalone components, lazy-loaded feature routes,
  signals, functional HttpInterceptorFn (csrf + auth), functional
  CanActivateFn auth guard, HttpOnly-cookie-based auth service.
- Tests: Jest + supertest, 46 tests across 13 suites covering
  migrations, env schema, theme loader, event status, login backoff,
  registration rate limit, ApiError shape, bootstrap integration,
  auth refresh rotation, admin guard, last-admin invariant, SSE flat
  payloads. Single-command runner: `npm test`.

tests/backend/api-error.spec.ts

@@ -0,0 +1,25 @@
+import { ApiError } from '../../backend/src/common/errors/api-error';
+import { ERROR_CODES } from '../../backend/src/common/errors/error-codes';
+
+describe('ApiError', () => {
+  it('formats validation errors with details', () => {
+    const e = ApiError.validation('Bad input', { field: 'x' });
+    expect(e.getStatus()).toBe(400);
+    const body = e.getResponse() as any;
+    expect(body.code).toBe(ERROR_CODES.VALIDATION_FAILED);
+    expect(body.message).toBe('Bad input');
+    expect(body.details).toEqual({ field: 'x' });
+  });
+
+  it('formats last-admin conflict', () => {
+    const e = ApiError.conflict(ERROR_CODES.LAST_ADMIN, 'Cannot delete the last admin');
+    expect(e.getStatus()).toBe(409);
+    const body = e.getResponse() as any;
+    expect(body.code).toBe(ERROR_CODES.LAST_ADMIN);
+  });
+
+  it('formats internal error as 500', () => {
+    const e = ApiError.internal();
+    expect(e.getStatus()).toBe(500);
+  });
+});