Without name = "...", the schema builder still produces the
auto-generated index_<table>_by_<cols> form. Sanity check that the
custom-name path doesn’t accidentally suppress all auto-naming.
#[key(name = "...", ...)] records the custom name on the primary-key
index in the DB schema. SQL backends emit primary keys inline today, so
this verifies the schema-internal wiring rather than DDL output.