- Add github.com/jackc/pgx/v5 v5.9.1 dependency
- Add golang-migrate pgx/v5 driver
- Create migrations/postgres/0001_initial_schema.up.sql with SERIAL PRIMARY KEY
- Create migrations/postgres/0001_initial_schema.down.sql
- Rename RunMigrations to RunSQLiteMigrations in migrate.go
- Add RunPostgresMigrations with pgxmigrate driver and 'pgx5' name
- Update export_test.go to use RunSQLiteMigrations (go vet compliance)
