- 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)
- RunMigrations applies versioned SQL files via golang-migrate + embed.FS (iofs)
- ErrNoChange handled correctly - not treated as failure
- Migration 0001 creates full current schema with CREATE TABLE IF NOT EXISTS
- All three tables (updates, tags, tag_assignments) with acknowledged_at and ON DELETE CASCADE
- Uses database/sqlite sub-package (modernc.org/sqlite, no CGO)
- go mod tidy applied after adding dependencies
