feat: add PostgreSQL persistence layer with Neon DB support

internal/db/migrate.go

@@ -0,0 +1,20 @@
+package db
+
+import (
+	"context"
+	_ "embed"
+	"fmt"
+
+	"github.com/jackc/pgx/v5/pgxpool"
+)
+
+//go:embed migrations/001_init.sql
+var initSQL string
+
+func Migrate(pool *pgxpool.Pool) error {
+	_, err := pool.Exec(context.Background(), initSQL)
+	if err != nil {
+		return fmt.Errorf("run migration: %w", err)
+	}
+	return nil
+}