feat(ntfy): Phase 2 — sendPushToUsers() ntfy 연동 + 구독 관리 UI

- ntfy_subscriptions 테이블 마이그레이션 추가
- ntfySender.js 유틸 (ntfy HTTP POST 래퍼)
- sendPushToUsers() ntfy 우선 분기 (ntfy 구독자 → ntfy, 나머지 → Web Push)
- ntfy subscribe/unsubscribe/status API 엔드포인트
- notification-bell.js ntfy 토글 버튼 + 앱 설정 안내 모달
- docker-compose system1-api에 NTFY 환경변수 추가

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

system1-factory/api/utils/ntfySender.js

@@ -0,0 +1,31 @@
+// utils/ntfySender.js — ntfy HTTP POST 래퍼
+const NTFY_BASE_URL = process.env.NTFY_BASE_URL || 'http://ntfy:80';
+const NTFY_PUBLISH_TOKEN = process.env.NTFY_PUBLISH_TOKEN;
+const TKFB_BASE_URL = process.env.TKFB_BASE_URL || 'https://tkfb.technicalkorea.net';
+
+async function sendNtfy(userId, { title, body, url }) {
+  if (!NTFY_PUBLISH_TOKEN) return;
+
+  const topic = `tkfactory-user-${userId}`;
+  const headers = {
+    'Authorization': `Bearer ${NTFY_PUBLISH_TOKEN}`,
+    'Title': title || '',
+    'Tags': 'bell',
+  };
+  if (url) {
+    headers['Click'] = url.startsWith('http') ? url : `${TKFB_BASE_URL}${url}`;
+  }
+
+  try {
+    const resp = await fetch(`${NTFY_BASE_URL}/${topic}`, {
+      method: 'POST',
+      headers,
+      body: body || '',
+    });
+    if (!resp.ok) console.warn(`[ntfy] ${userId} 발송 실패: ${resp.status}`);
+  } catch (e) {
+    console.error(`[ntfy] ${userId} 발송 오류:`, e.message);
+  }
+}
+
+module.exports = { sendNtfy };