feat: add PostgreSQL migration runner

server/cmd/migrate/main.go

@@ -0,0 +1,36 @@
+package main
+
+import (
+	"context"
+	"database/sql"
+	"flag"
+	"fmt"
+	"os"
+	"time"
+
+	"github.com/cosmic-clash/cosmic-clash/server/migrations"
+	_ "github.com/jackc/pgx/v5/stdlib"
+)
+
+func main() {
+	dsn := flag.String("dsn", os.Getenv("COSMIC_CLASH_POSTGRES_DSN"), "PostgreSQL connection string")
+	directory := flag.String("dir", "migrations", "directory containing numbered SQL migrations")
+	flag.Parse()
+	if *dsn == "" {
+		fmt.Fprintln(os.Stderr, "migrate: --dsn or COSMIC_CLASH_POSTGRES_DSN is required")
+		os.Exit(2)
+	}
+	db, err := sql.Open("pgx", *dsn)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, "migrate:", err)
+		os.Exit(1)
+	}
+	defer db.Close()
+	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
+	defer cancel()
+	if err := migrations.Apply(ctx, db, *directory); err != nil {
+		fmt.Fprintln(os.Stderr, "migrate:", err)
+		os.Exit(1)
+	}
+	fmt.Println("migrations applied")
+}