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>

infra/.env.example

@@ -16,3 +16,11 @@ ACS_SMS_API_URL=http://210.104.132.59:8000
 # URL the SMS link points to — MUST be reachable from the visitor's phone
 # (the server's real address/domain, not localhost). e.g. https://acs.example.co.kr
 ACS_PUBLIC_BASE_URL=http://localhost
+
+# ===== Security =====
+# CORS allowed origins (comma-separated). Leave EMPTY when web+API share one origin
+# via nginx (default). Set only if the SPA is hosted on a different origin.
+ACS_CORS_ALLOWED_ORIGINS=
+# Set to true ONLY when the site is served over HTTPS — marks the session cookie Secure.
+# Leaving it false over plain http keeps login working; true over http would break it.
+ACS_COOKIE_SECURE=false

infra/docker-compose.yml

@@ -28,6 +28,9 @@ services:
       ACS_SMS_PROVIDER: ${ACS_SMS_PROVIDER:-dev}
       ACS_SMS_API_URL: ${ACS_SMS_API_URL:-http://210.104.132.59:8000}
       ACS_PUBLIC_BASE_URL: ${ACS_PUBLIC_BASE_URL:-http://localhost}
+      # Security: CORS origins (empty = same-origin via nginx); cookie Secure (enable under HTTPS)
+      ACS_CORS_ALLOWED_ORIGINS: ${ACS_CORS_ALLOWED_ORIGINS:-}
+      ACS_COOKIE_SECURE: ${ACS_COOKIE_SECURE:-false}
     depends_on:
       - db
     networks: