feat: ✨ implement custom proxy subscription management and enhance configuration

- Added support for importing Clash/V2ray subscriptions, including automatic format detection and integration with sing-box for protocol conversion.
- Introduced five proxy usage modes in the configuration, allowing flexible selection between mixed, custom-only, and free-only modes.
- Enhanced `.env.example` and `docker-compose.yml` to include new environment variables for custom proxy settings.
- Updated `CHANGELOG.md` to document new features and improvements related to subscription management.
- Improved WebUI for managing subscriptions and displaying proxy statistics.
- Implemented a background process for refreshing subscriptions and probing disabled proxies for reactivation.

checker/health_checker.go

@@ -78,9 +78,14 @@ func (hc *HealthChecker) RunOnce() {
 		} else {
 			// 失败次数+1
 			hc.storage.IncrementFailCount(result.Proxy.Address)
-			// 如果失败次数 >= 3，删除
+			// 如果失败次数 >= 3
 			if result.Proxy.FailCount+1 >= 3 {
-				hc.storage.Delete(result.Proxy.Address)
+				if result.Proxy.Source == "custom" {
+					// 订阅代理：禁用而非删除
+					hc.storage.DisableProxy(result.Proxy.Address)
+				} else {
+					hc.storage.Delete(result.Proxy.Address)
+				}
 				removeCount++
 			}
 		}