fix(security): P0 — CSRF 방어, h2-console prod 격리, CORS 외부화

- CSRF: CookieCsrfTokenRepository(이중제출 토큰) + SPA용 CsrfTokenRequestAttributeHandler,
  CsrfCookieFilter로 XSRF-TOKEN 쿠키 강제 렌더. /api/auth/login·/api/public/** 는 예외.
  프론트 api.ts가 변경요청에 X-XSRF-TOKEN 헤더 자동 주입.
- 세션쿠키 SameSite=Lax·HttpOnly, prod는 Secure=${ACS_COOKIE_SECURE:false}(HTTPS 시 활성).
- h2-console permitAll·frameOptions.sameOrigin을 spring.h2.console.enabled에 연동 → prod 자동 비노출.
- CORS allowed-origins를 acs.cors.allowed-origins 프로퍼티로 외부화(prod 기본 빈 값, nginx 동일출처).
- .env.example·docker-compose에 ACS_CORS_ALLOWED_ORIGINS·ACS_COOKIE_SECURE 추가.

검증: 빌드/테스트 통과, curl로 CSRF 차단(403)·토큰 통과(404)·로그인/공개 예외·dev h2-console 확인.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/api.ts

@@ -21,10 +21,22 @@ const BASE = '/api';
 /** Endpoints whose 401 must NOT trigger a redirect (login probe / public pages). */
 const NO_REDIRECT_ON_401 = ['/auth/me', '/auth/login', '/auth/logout', '/public/'];
 
+/**
+ * CSRF double-submit: the backend sets an XSRF-TOKEN cookie; echo it back in the
+ * X-XSRF-TOKEN header on state-changing requests. GET/HEAD need no token.
+ */
+function csrfHeaders(method?: string): Record<string, string> {
+  const m = (method ?? 'GET').toUpperCase();
+  if (m === 'GET' || m === 'HEAD') return {};
+  const c = document.cookie.match(/(?:^|;\s*)XSRF-TOKEN=([^;]+)/);
+  return c ? { 'X-XSRF-TOKEN': decodeURIComponent(c[1]) } : {};
+}
+
 async function request<T>(path: string, init?: RequestInit): Promise<T> {
   const res = await fetch(`${BASE}${path}`, {
     credentials: 'include',
     ...init,
+    headers: { ...(init?.headers ?? {}), ...csrfHeaders(init?.method) },
   });
   // Session expired / not authenticated on a protected call → send to login.
   if (