feat: 인턴 직급 + 초과근무 관리자 집계화 + SSO 로그아웃 URL + 디바이스/FCM

- 직급에 인턴 추가(기본 할당량 15), 직책(position)은 UI에서 제거(컬럼은 유지)
- 초과근무: 유저 신청 제거 → 관리자 근무관리에서 실제 출퇴근 기록 기반 자동 집계
- 로그아웃: infra 공통 LOGOUT_URL(/me로 전달) 사용 → oauth2-proxy 종료 + Keycloak end-session
- (이전 커밋 포함) Device 등록 + FCM HTTP v1 sender + notify 연동

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/config/config.go

@@ -24,6 +24,13 @@ type Config struct {
 	S3SecretKey      string
 	DevAuth          bool
 	SeedData         bool
+	// FCMCredentialsFile is the path to a Firebase service-account JSON used to
+	// send push notifications to spin-mobile. Empty = push disabled (no-op).
+	FCMCredentialsFile string
+	// LogoutURL is the common SSO logout path injected by infra (LOGOUT_URL):
+	// ends the oauth2-proxy session then redirects to Keycloak end-session.
+	// The static frontend reads it via /me. Defaults to the infra-common value.
+	LogoutURL string
 	// AdminGroups are the Keycloak groups whose members are super-admins
 	// (manage everything across the company: incentive console, accounting,
 	// approvals, all member/project data).
@@ -69,7 +76,10 @@ func Load() Config {
 		SeedData: env("SEED", "false") == "true",
 		// Super-admin Keycloak groups (comma-separated). Default: admin
 		// (shared group name across all internal apps, not app-specific).
-		AdminGroups: splitCSV(env("ADMIN_GROUPS", "admin")),
+		AdminGroups:        splitCSV(env("ADMIN_GROUPS", "admin")),
+		FCMCredentialsFile: env("FCM_CREDENTIALS_FILE", ""),
+		LogoutURL: env("LOGOUT_URL",
+			"/oauth2/sign_out?rd=https%3A%2F%2Fauth.special-partners.com%2Frealms%2Fsp%2Fprotocol%2Fopenid-connect%2Flogout"),
 	}
 }