Identify missing or incorrect indexes on the PostgreSQL schema — foreign keys without indexes, columns used in frequent WHERE/JOIN/ORDER BY clauses that lack one, and redundant indexes wasting write performance. Use when adding a new query pattern (especially search/filter/analytics endpoints), when the user asks why a query feels slow, or when reviewing a new Alembic migration that adds a foreign key (pair with database-migration-safety, which already flagged this project's recent migration added four missing trainer FK indexes — this skill is the general-purpose version of that same check).
