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/api/v1/problems.py

@@ -363,6 +363,7 @@ def resolve_problem(
         raise HTTPException(status_code=409, detail="Problem already resolved")
 
     problem.status = "resolved"
+    problem.resolved_by = "manual"
 
     db.commit()