refactor: split backend into standalone server project

Remove embedded frontend and workflow editor assets, add standalone API deployment configuration, and retain the current backend service updates.

internal/bootstrap/db.go

@@ -12,6 +12,7 @@ import (
 
 	"github.com/mlogclub/simple/sqls"
 	"gorm.io/driver/mysql"
+	"gorm.io/driver/postgres"
 
 	// "gorm.io/driver/sqlite" // Sqlite driver based on CGO
 	"github.com/glebarez/sqlite" // Pure go SQLite driver, checkout https://github.com/glebarez/sqlite for details
@@ -23,17 +24,9 @@ import (
 )
 
 func InitDB(cfg config.DBConfig) (*gorm.DB, error) {
-	var dialector gorm.Dialector
-	switch cfg.Type {
-	case "sqlite":
-		if err := ensureSQLiteDir(cfg.DSN); err != nil {
-			return nil, err
-		}
-		dialector = sqlite.Open(cfg.DSN)
-	case "mysql":
-		dialector = mysql.Open(cfg.DSN)
-	default:
-		return nil, fmt.Errorf("unsupported db type: %s", cfg.Type)
+	dialector, err := newDialector(cfg)
+	if err != nil {
+		return nil, err
 	}
 
 	db, err := gorm.Open(dialector, &gorm.Config{
@@ -76,6 +69,22 @@ func InitDB(cfg config.DBConfig) (*gorm.DB, error) {
 	return db, nil
 }
 
+func newDialector(cfg config.DBConfig) (gorm.Dialector, error) {
+	switch strings.ToLower(strings.TrimSpace(cfg.Type)) {
+	case "sqlite":
+		if err := ensureSQLiteDir(cfg.DSN); err != nil {
+			return nil, err
+		}
+		return sqlite.Open(cfg.DSN), nil
+	case "mysql":
+		return mysql.Open(cfg.DSN), nil
+	case "postgres", "postgresql":
+		return postgres.Open(cfg.DSN), nil
+	default:
+		return nil, fmt.Errorf("unsupported db type: %s", cfg.Type)
+	}
+}
+
 func ensureSQLiteDir(dsn string) error {
 	dbPath := sqliteFilePath(dsn)
 	if dbPath == "" {