Fix build and run issues

internal/db/db.go

@@ -3,9 +3,10 @@ package db
 import (
 	"context"
 	"database/sql"
+	"errors"
 	"fmt"
 
-	_ "github.com/go-sql-driver/mysql"
+	"github.com/go-sql-driver/mysql"
 )
 
 func Open(dsn string) (*sql.DB, error) {
@@ -22,6 +23,10 @@ func Open(dsn string) (*sql.DB, error) {
 func Migrate(ctx context.Context, db *sql.DB) error {
 	for _, stmt := range statements {
 		if _, err := db.ExecContext(ctx, stmt); err != nil {
+			var mysqlErr *mysql.MySQLError
+			if errors.As(err, &mysqlErr) && mysqlErr.Number == 1060 {
+				continue // duplicate column — already exists
+			}
 			return fmt.Errorf("migrate: %w", err)
 		}
 	}