fix: enforce durable migration ownership and readiness

hub_core/migrations/roles.py

@@ -0,0 +1,12 @@
+from __future__ import annotations
+
+import re
+
+
+def migration_role_statement(role: str | None) -> str | None:
+    """Return a safely quoted SET ROLE statement for an admitted owner role."""
+    if not role:
+        return None
+    if not re.fullmatch(r"[a-z_][a-z0-9_]{0,62}", role):
+        raise ValueError("HUB_CORE_MIGRATION_ROLE is not a safe PostgreSQL role name")
+    return f'SET ROLE "{role}"'