- register_group() accepts $args['indexes'] (name => ordered keys); indexes on
unknown keys are dropped. Kept outside the field definition, so schema
hashes are unchanged.
- Schema_Manager::ensure_group_indexes() adds missing cidx_* indexes to the
existing flat table in place; the applied definition is remembered in
tmdo_entity_indexes so later requests skip SHOW INDEX.
- Bench (1M listings, scenario 2): Entity p50 337 ms -> 278 ms with
(hp_verified, hp_price), on par with Hot (269 ms).
- Verify: core unit 656 / integration 459 green, phpcs clean
- PR: PR-027
