fix(migrator): honor DatabaseURL connection string in v3 migrator

The v3->v4 migrator built its DSN from component fields only, ignoring
DatabaseURL - so configs that set only a connection string (required
for postgres unix sockets, e.g. "host=/var/run/postgresql dbname=...")
fell back to a host/port DSN and failed to connect. The migrator now
reads DatabaseURL and passes it to gorm verbatim, matching the main
client. Closes #42.

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

application/migrator/conf/conf.go

@@ -18,6 +18,7 @@ type database struct {
 	Port        int
 	Charset     string
 	UnixSocket  bool
+	DatabaseURL string
 }
 
 // system 系统通用配置

application/migrator/model/init.go

@@ -34,6 +34,16 @@ func Init() error {
 		confDBType = "mysql"
 	}
 
+	// A full connection string overrides component fields - required for
+	// postgres unix sockets ("host=/var/run/postgresql dbname=..."), which
+	// the component fields cannot express.
+	if conf.DatabaseConfig.DatabaseURL != "" {
+		dialect := confDBType
+		if dialect == "UNSET" || dialect == "sqlite" {
+			dialect = "sqlite3"
+		}
+		db, err = gorm.Open(dialect, conf.DatabaseConfig.DatabaseURL)
+	} else {
 		switch confDBType {
 		case "UNSET", "sqlite":
 			// 未指定数据库或者明确指定为 sqlite 时，使用 SQLite 数据库
@@ -65,6 +75,7 @@ func Init() error {
 		default:
 			return fmt.Errorf("unsupported database type %q", confDBType)
 		}
+	}
 
 	//db.SetLogger(util.Log())
 	if err != nil {