- Simplify bootstrapMigrationsTable to just check table existence and
apply 000.sql if missing — no legacy DB detection
- Remove ensureBootstrapVersionRecorded (legacy backfill path)
- Remove applyBootstrapMigration (separate helper, now inlined)
- Remove TestBootstrapMigrationsTable_ExistingTableBackwardsCompat
- Simplify 000.sql header comment