feat: proactive host_silence scan for stale agent.heartbeat (0.8.3)

Background scan every 5 min opens rule:host_silence and notifies without
waiting for the next ingest event. CLI job + optional systemd timer.

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

deploy/env.native.example

@@ -63,6 +63,10 @@ SAC_DAILY_REPORT_REQUIRE_ACTIVITY=true
 # Статус хоста по agent.heartbeat
 SAC_HEARTBEAT_STALE_MINUTES=780
 
+# Проактивный алерт host_silence (без ожидания нового события с хоста)
+SAC_HOST_SILENCE_SCAN_ENABLED=true
+SAC_HOST_SILENCE_SCAN_INTERVAL_MINUTES=5
+
 # Корреляция Problems: host + type + rule в одном open Problem (минуты)
 SAC_PROBLEM_CORRELATION_WINDOW_MINUTES=60