export-db.py never renders indexes into schema.md (dead query_indexes assignment) — schema.md has understated indexes since always

db-mars-cc flagged during MARS-537. The schema exporter (export-db.py) assigns query_indexes but never renders it into schema.md, so the committed schema.md has understated index coverage since inception. Pre-existing, low-sev doc-fidelity bug. Fix = render indexes into schema.md; note a one-time index backfill will balloon schema.md. db authors in-lane. Greenlit — tracking only for the diff-size heads-up.