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/pkg/config/config.go

@@ -42,8 +42,9 @@ type WxWorkNotifyConfig struct {
 }
 
 type ServerConfig struct {
-	Port int        `yaml:"port"`
-	CORS CORSConfig `yaml:"cors"`
+	Port        int        `yaml:"port"`
+	FrontendURL string     `yaml:"frontendUrl"`
+	CORS        CORSConfig `yaml:"cors"`
 }
 
 func (s ServerConfig) Address() string {
@@ -53,6 +54,13 @@ func (s ServerConfig) Address() string {
 	return fmt.Sprintf(":%d", s.Port)
 }
 
+func (s ServerConfig) FrontendBaseURL() string {
+	if value := strings.TrimRight(strings.TrimSpace(s.FrontendURL), "/"); value != "" {
+		return value
+	}
+	return "http://127.0.0.1:3000"
+}
+
 type CORSConfig struct {
 	// AllowedOrigins 是允许浏览器跨域访问的 Origin 白名单，必须包含协议和域名。
 	// 留空表示不允许跨域请求；同源请求通常不会携带 Origin，不受影响。