feat: webhook notification channel with UI and ingest dispatch

Add webhook config (DB/env), JSON POST on events/problems, settings API,
Settings UI section, and notify_dispatch for multi-channel ingest.

Co-authored-by: Cursor <cursoragent@cursor.com>

deploy/env.native.example

@@ -25,7 +25,14 @@ TELEGRAM_CHAT_ID=
 # exclusive: warning (failed login, problems); prod noise-only: high
 TELEGRAM_MIN_SEVERITY=high
 
-# Статус хоста по agent.heartbeat (минуты; ssh-monitor шлёт ~раз в 12 ч)
+# Generic webhook (JSON POST), F-NOT-01
+WEBHOOK_ENABLED=false
+WEBHOOK_URL=
+WEBHOOK_SECRET_HEADER=
+WEBHOOK_SECRET=
+WEBHOOK_MIN_SEVERITY=high
+
+# Статус хоста по agent.heartbeat
 SAC_HEARTBEAT_STALE_MINUTES=780
 
 # Корреляция Problems: host + type + rule в одном open Problem (минуты)