✨ feat(bdd): parallel-safe schema-per-package isolation (T12 stage 2/2) — 2.85x speedup (#35)

Per-package isolated Postgres schema with migrations. Local benchmark: 12.87s sequential → 4.51s parallel = 2.85x. ADR-0025 status to Implemented. CI uses BDD_SCHEMA_ISOLATION=true.

Co-authored-by: Gabriel Radureau <arcodange@gmail.com>
Co-committed-by: Gabriel Radureau <arcodange@gmail.com>

pkg/user/postgres_repository.go

@@ -184,7 +184,15 @@ func BuildSchemaIsolatedDSN(cfg *config.Config, schemaName string) string {
 	)
 }
 
-// (Close already exists below; we reuse it.)
+// Exec runs a raw SQL statement against the repository's connection.
+// Used by BDD test infra for schema lifecycle (CREATE SCHEMA / DROP SCHEMA).
+// Avoid in production code paths -- prefer the typed Repository methods.
+func (r *PostgresRepository) Exec(sql string) error {
+	if r.db == nil {
+		return fmt.Errorf("Exec called on PostgresRepository with nil db")
+	}
+	return r.db.Exec(sql).Error
+}
 
 // initializeDatabase sets up the PostgreSQL database connection and runs migrations
 func (r *PostgresRepository) initializeDatabase() error {