feat: 新增文件上传服务

- 添加 UploadHandler 处理文件上传
- 添加 UploadService 实现文件存储
- 配置上传文件大小限制和存储路径

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/internal/config/config.go

@@ -15,7 +15,17 @@ type Config struct {
 	Port              string
 	JWTSecret         string
 	DatabaseURL       string
-	PythonServiceURL string
+	PythonServiceURL  string
+	// 文件上传配置
+	UploadMode      string // "local" 或 "minio"
+	UploadLocalPath string // 本地存储路径，如 "resource/files"
+	ServerBaseURL   string // 服务器基础 URL，用于生成本地文件 URL
+	// MinIO 配置
+	MinIOEndpoint   string
+	MinIOAccessKey  string
+	MinIOSecretKey  string
+	MinIOBucket     string
+	MinIOUseSSL    bool
 }
 
 func Load() *Config {
@@ -30,16 +40,35 @@ func Load() *Config {
 	viper.SetDefault("jwt_secret", "your-secret-key-change-in-production")
 	viper.SetDefault("python_service_url", "http://localhost:8081")
 	viper.SetDefault("database_url", "root:root@tcp(localhost:3306)/x_agents?charset=utf8mb4&parseTime=True&loc=Local")
+	// 文件上传默认配置
+	viper.SetDefault("upload_mode", "local")
+	viper.SetDefault("upload_local_path", "resource/files")
+	viper.SetDefault("server_base_url", "http://localhost:8080")
+	viper.SetDefault("minio_endpoint", "localhost:9000")
+	viper.SetDefault("minio_access_key", "")
+	viper.SetDefault("minio_secret_key", "")
+	viper.SetDefault("minio_bucket", "x-agents")
+	viper.SetDefault("minio_use_ssl", false)
 
 	if err := viper.ReadInConfig(); err != nil {
 		log.Printf("Using default config: %v", err)
 	}
 
 	return &Config{
-		Port:              viper.GetString("port"),
-		JWTSecret:         viper.GetString("jwt_secret"),
-		DatabaseURL:       viper.GetString("database_url"),
+		Port:             viper.GetString("port"),
+		JWTSecret:        viper.GetString("jwt_secret"),
+		DatabaseURL:      viper.GetString("database_url"),
 		PythonServiceURL: viper.GetString("python_service_url"),
+		// 文件上传配置
+		UploadMode:      viper.GetString("upload_mode"),
+		UploadLocalPath: viper.GetString("upload_local_path"),
+		ServerBaseURL:   viper.GetString("server_base_url"),
+		// MinIO 配置
+		MinIOEndpoint:  viper.GetString("minio_endpoint"),
+		MinIOAccessKey: viper.GetString("minio_access_key"),
+		MinIOSecretKey: viper.GetString("minio_secret_key"),
+		MinIOBucket:    viper.GetString("minio_bucket"),
+		MinIOUseSSL:    viper.GetBool("minio_use_ssl"),
 	}
 }