feat: Problems correlation fingerprint, count, last_seen (d1-2)

- Migration 003; windowed host+type+rule correlation on ingest

- GET /problems filters; GET /problems/{id} with event timeline; ack/resolve 409 guard

- Tests and SAC_PROBLEM_CORRELATION_WINDOW_MINUTES config

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

deploy/env.native.example

@@ -26,4 +26,7 @@ TELEGRAM_MIN_SEVERITY=high
 # Статус хоста по agent.heartbeat (минуты; ssh-monitor шлёт ~раз в 12 ч)
 SAC_HEARTBEAT_STALE_MINUTES=780
 
+# Корреляция Problems: host + type + rule в одном open Problem (минуты)
+SAC_PROBLEM_CORRELATION_WINDOW_MINUTES=60
+
 CORS_ORIGINS=*