fix(i18n): Add missing incident.systemStable and activeAlerts translations

Fixes translation key leak in production UI.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/web/messages/en.json

@@ -153,6 +153,8 @@
     "title": "Incident Management",
     "activeIncidents": "Active Incidents",
     "noActiveIncidents": "No active incidents",
+    "systemStable": "System Stable",
+    "activeAlerts": "active alerts",
     "signals": "signals",
     "proposals": "proposals",
     "affectedServices": "Affected Services",

apps/web/messages/zh-TW.json

@@ -153,6 +153,8 @@
     "title": "事件管理",
     "activeIncidents": "活躍事件",
     "noActiveIncidents": "目前無活躍事件",
+    "systemStable": "系統穩定",
+    "activeAlerts": "筆活躍告警",
     "signals": "筆告警",
     "proposals": "筆提案",
     "affectedServices": "受影響服務",