Pin the SQLAlchemy enum-naming invariant: every column typed Role
(aliased as AgentRole) MUST bind to the postgres enum named
'agentrole', not 'role'. Wave A5's smoke regression came from the
inferred 'role' type colliding with migration 001's 'agentrole'.
The fix already shipped (roboco/db/tables.py::_PG_ENUM_NAME_OVERRIDES);
this test locks it in. Two assertions: agents.role.udt_name == agentrole;
no stray 'role' enum type exists in pg_type.
