Harden scaffold (reviewer followups)

- main.ts awaits DatabaseInitService.init() before app.listen(), ensuring
  migrations + seed run before the HTTP server accepts traffic.
- AppModule now uses NestModule with consumer.apply() no longer needed for
  CSRF (registered globally via app.use after body parsers in main.ts).
- JwtAuthGuard extended from AuthGuard('jwt') so protected endpoints
  actually validate the bearer token.
- Admin controller now uses Zod-validated DTOs for body/path/query:
  createUser, updateUserRole, userIdParam, listUsersQuery; with @Public
  / @Roles decorators and AdminGuard applied.
- Multer upload module + controller (POST /api/v1/uploads/category-icon
  and /challenge-file) with safe-filename strategy, configured
  UPLOAD_SIZE_LIMIT, admin-only via AdminGuard, served via /uploads
  static handler.
- ThemeLoaderService now requires all 10 canonical theme ids at startup,
  backfilling missing themes from built-ins with a warning; validates the
  configured themeKey setting and falls back to 'classic' if invalid;
  gracefully tolerates missing setting table during early boot.
- Test suite expanded to 76 tests / 17 suites; new specs:
  admin-validation, uploads, theme-required, database-init.

tests/frontend/theme.spec.ts

@@ -19,9 +19,11 @@ describe('ThemeLoaderService builtins', () => {
 
   it('falls back to default for unknown id', () => {
     const config = { get: jest.fn((k: string, d: any) => d) } as any;
-    const svc = new ThemeLoaderService(config);
-    svc.onModuleInit();
-    const t = svc.getTheme('totally-unknown');
-    expect(t.id).toBe('classic');
+    const settings = { get: jest.fn().mockResolvedValue('classic') } as any;
+    const svc = new ThemeLoaderService(config, settings);
+    return svc.onModuleInit().then(() => {
+      const t = svc.getTheme('totally-unknown');
+      expect(t.id).toBe('classic');
+    });
   });
 });