fix: 12h cooldown before reopening manually closed host_silence (0.9.9)

Track resolved_by on problems; suppress scan/ingest recreate after manual
resolve; reopen same problem after cooldown; auto-close via heartbeat unchanged.

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

backend/app/services/problem_rules.py

@@ -190,6 +190,7 @@ def resolve_host_silence_problems(db: Session, host_id: int) -> int:
     ).all()
     for problem in problems:
         problem.status = "resolved"
+        problem.resolved_by = "auto"
     if problems:
         db.flush()
     return len(problems)