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/models/pushSubscriptionModel.js

@@ -46,6 +46,46 @@ const pushSubscriptionModel = {
   async deleteByEndpoint(endpoint) {
     const db = await getDb();
     await db.query('DELETE FROM push_subscriptions WHERE endpoint = ?', [endpoint]);
+  },
+
+  // === ntfy 구독 관련 ===
+
+  async getNtfyUserIds(userIds) {
+    if (!userIds || userIds.length === 0) return [];
+    const db = await getDb();
+    const [rows] = await db.query(
+      'SELECT user_id FROM ntfy_subscriptions WHERE user_id IN (?)',
+      [userIds]
+    );
+    return rows.map(r => r.user_id);
+  },
+
+  async getAllNtfyUserIds() {
+    const db = await getDb();
+    const [rows] = await db.query('SELECT user_id FROM ntfy_subscriptions');
+    return rows.map(r => r.user_id);
+  },
+
+  async ntfySubscribe(userId) {
+    const db = await getDb();
+    await db.query(
+      'INSERT IGNORE INTO ntfy_subscriptions (user_id) VALUES (?)',
+      [userId]
+    );
+  },
+
+  async ntfyUnsubscribe(userId) {
+    const db = await getDb();
+    await db.query('DELETE FROM ntfy_subscriptions WHERE user_id = ?', [userId]);
+  },
+
+  async isNtfySubscribed(userId) {
+    const db = await getDb();
+    const [rows] = await db.query(
+      'SELECT 1 FROM ntfy_subscriptions WHERE user_id = ? LIMIT 1',
+      [userId]
+    );
+    return rows.length > 0;
   }
 };