Add media proxy feature for resource downloading

- Introduced a new API endpoint `GET /api/v1/video/proxy` to facilitate media resource downloads, allowing users to bypass domain restrictions imposed by WeChat.
- Updated configuration to include proxy settings such as `SHORT_VIDEO_PROXY_ENABLED`, `SHORT_VIDEO_PROXY_ALLOWED_DOMAINS`, `SHORT_VIDEO_PROXY_MAX_SIZE_MB`, and `SHORT_VIDEO_PROXY_TIMEOUT_SECONDS`.
- Enhanced the `ShortVideoConfig` struct to accommodate new proxy-related fields.
- Improved error handling for proxy requests, including checks for allowed domains and file size limits.
- Updated documentation to reflect the new proxy functionality and its configuration options, ensuring clarity for users and developers.

config/config.go

@@ -49,6 +49,11 @@ type ShortVideoConfig struct {
 	APIKey         string
 	FreeDailyQuota int
 	RequestTimeout time.Duration
+	// 代理相关配置
+	ProxyEnabled        bool          // 是否启用媒体代理
+	ProxyAllowedDomains []string      // 允许代理的域名白名单（为空表示允许所有）
+	ProxyMaxSize        int64         // 代理文件最大大小（字节），0 表示不限制
+	ProxyTimeout        time.Duration // 代理请求超时时间
 }
 
 // AIConfig 用于“AI 建议/问答”等能力的通用配置（OpenAI-compatible）。
@@ -122,9 +127,13 @@ func LoadConfig() {
 			Expire: 86400, // 24小时
 		},
 		ShortVideo: ShortVideoConfig{
-			APIKey:         getEnv("SHORT_VIDEO_API_KEY", ""),
-			FreeDailyQuota: getEnvAsInt("SHORT_VIDEO_FREE_QUOTA", 20),
-			RequestTimeout: time.Duration(getEnvAsInt("SHORT_VIDEO_TIMEOUT_SECONDS", 5)) * time.Second,
+			APIKey:              getEnv("SHORT_VIDEO_API_KEY", ""),
+			FreeDailyQuota:      getEnvAsInt("SHORT_VIDEO_FREE_QUOTA", 20),
+			RequestTimeout:      time.Duration(getEnvAsInt("SHORT_VIDEO_TIMEOUT_SECONDS", 5)) * time.Second,
+			ProxyEnabled:        getEnvAsBool("SHORT_VIDEO_PROXY_ENABLED", true),
+			ProxyAllowedDomains: getEnvAsStringSlice("SHORT_VIDEO_PROXY_ALLOWED_DOMAINS", nil),
+			ProxyMaxSize:        int64(getEnvAsInt("SHORT_VIDEO_PROXY_MAX_SIZE_MB", 100)) * 1024 * 1024,
+			ProxyTimeout:        time.Duration(getEnvAsInt("SHORT_VIDEO_PROXY_TIMEOUT_SECONDS", 60)) * time.Second,
 		},
 		AI: AIConfig{
 			BaseURL:        getEnv("AI_BASE_URL", "https://api.openai.com/v1"),
@@ -198,3 +207,28 @@ func getEnvAsInt(key string, defaultValue int) int {
 	}
 	return defaultValue
 }
+
+func getEnvAsBool(key string, defaultValue bool) bool {
+	if value := os.Getenv(key); value != "" {
+		v := strings.ToLower(value)
+		return v == "true" || v == "1" || v == "yes"
+	}
+	return defaultValue
+}
+
+func getEnvAsStringSlice(key string, defaultValue []string) []string {
+	if value := os.Getenv(key); value != "" {
+		parts := strings.Split(value, ",")
+		result := make([]string, 0, len(parts))
+		for _, part := range parts {
+			trimmed := strings.TrimSpace(part)
+			if trimmed != "" {
+				result = append(result, trimmed)
+			}
+		}
+		if len(result) > 0 {
+			return result
+		}
+	}
+	return defaultValue
+}