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/alembic/versions/015_problem_resolved_by.py

@@ -0,0 +1,26 @@
+"""problems.resolved_by — manual vs auto close for host_silence cooldown
+
+Revision ID: 015
+Revises: 014
+"""
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "015"
+down_revision: Union[str, None] = "014"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "problems",
+        sa.Column("resolved_by", sa.String(length=16), nullable=True),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("problems", "resolved_by")