feat(monitoring): Plan C 外部網站告警 — 4個網站 + SSL憑證預警

新增 external_website_alerts 群組：
- MoWoooWorkDown (mo.wooo.work, 188, momo-app)
- TsenyangWebsiteDown (tsenyang.com, 188, tsenyang-website)
- StockWoooWorkDown (stock.wooo.work, 110, stock-platform)
- BitanWoooWorkDown (bitan.wooo.work, 188, bitan-app)
- ExternalSiteSSLExpiringSoon (14天預警, auto_repair:false)

blackbox-http 已涵蓋全部目標，此為結構化告警規則。

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

ops/monitoring/alerts-unified.yml

@@ -542,3 +542,79 @@ groups:
         annotations:
           summary: "Kali Scanner 離線"
           description: "Kali (192.168.0.112:8080) 離線，安全掃描功能暫停"
+
+  # =========================================================================
+  # Plan C — 外部網站監控 (Sprint 5.2, 2026-04-09 Claude Sonnet 4.6 Asia/Taipei)
+  # blackbox-http 已涵蓋 4 個外部網站，此群組提供結構化告警
+  # auto_repair: "true" — 由 AWOOOI Guardrail 決策（Service Registry 分級）
+  # =========================================================================
+  - name: external_website_alerts
+    rules:
+      - alert: MoWoooWorkDown
+        expr: probe_success{job="blackbox-http", instance="https://mo.wooo.work"} == 0
+        for: 3m
+        labels:
+          severity: critical
+          layer: external
+          component: momo-app
+          host: "188"
+          team: ops
+          auto_repair: "true"
+        annotations:
+          summary: "外部網站 mo.wooo.work 離線"
+          description: "mo.wooo.work 探測失敗超過 3 分鐘，容器 momo-app (188) 可能需要重啟"
+
+      - alert: TsenyangWebsiteDown
+        expr: probe_success{job="blackbox-http", instance="https://www.tsenyang.com"} == 0
+        for: 3m
+        labels:
+          severity: critical
+          layer: external
+          component: tsenyang-website
+          host: "188"
+          team: ops
+          auto_repair: "true"
+        annotations:
+          summary: "外部網站 tsenyang.com 離線"
+          description: "tsenyang.com 探測失敗超過 3 分鐘，容器 tsenyang-website (188) 可能需要重啟"
+
+      - alert: StockWoooWorkDown
+        expr: probe_success{job="blackbox-http", instance="http://stock.wooo.work"} == 0
+        for: 3m
+        labels:
+          severity: critical
+          layer: external
+          component: stock-platform
+          host: "110"
+          team: ops
+          auto_repair: "true"
+        annotations:
+          summary: "外部網站 stock.wooo.work 離線"
+          description: "stock.wooo.work 探測失敗超過 3 分鐘，容器 stock-platform (110) 可能需要重啟"
+
+      - alert: BitanWoooWorkDown
+        expr: probe_success{job="blackbox-http", instance="https://bitan.wooo.work"} == 0
+        for: 3m
+        labels:
+          severity: critical
+          layer: external
+          component: bitan-app
+          host: "188"
+          team: ops
+          auto_repair: "true"
+        annotations:
+          summary: "外部網站 bitan.wooo.work 離線"
+          description: "bitan.wooo.work 探測失敗超過 3 分鐘，容器 bitan-app (188) 可能需要重啟"
+
+      - alert: ExternalSiteSSLExpiringSoon
+        expr: probe_ssl_earliest_cert_expiry{job="blackbox-http"} - time() < 14 * 24 * 3600
+        for: 1h
+        labels:
+          severity: warning
+          layer: external
+          component: ssl
+          team: ops
+          auto_repair: "false"
+        annotations:
+          summary: "SSL 憑證即將到期: {{ $labels.instance }}"
+          description: "{{ $labels.instance }} SSL 憑證將在 14 天內到期，請手動更新"