fix: add missing migration for probe_result column

Adds probe_result JSON column to tool_instances table.
This column stores readiness probe results and was added to the
model but the migration was missing.

apps/api/alembic/versions/0013_add_probe_result.py

@@ -0,0 +1,29 @@
+"""add probe_result to tool_instances
+
+Revision ID: 0013_add_probe_result
+Revises: 0012_default_port_req
+Create Date: 2026-05-22 21:45:00.000000
+
+"""
+from typing import Sequence, Union
+
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects import postgresql
+
+# revision identifiers, used by Alembic.
+revision: str = "0013_add_probe_result"
+down_revision: Union[str, None] = "0012_default_port_req"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "tool_instances",
+        sa.Column("probe_result", postgresql.JSON, nullable=True)
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("tool_instances", "probe_result")