fix

Opt-in writer (the /claude-db:fix command). Applies the safe, reversible schema/migration changes from an audit — adding indexes, NOT NULL/CHECK/UNIQUE constraints, missing FKs, type corrections, default/generated columns — as expand-contract migrations. Dry-run preview by default; writes only after explicit per-change confirmation, and only via the migration-writer subagent. Runs only when the user invokes it —…