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.

docker-compose.yml

@@ -26,8 +26,10 @@ services:
       - PROXY_AUTH_PASSWORD=${PROXY_AUTH_PASSWORD}
       - BLOCKED_COUNTRIES=${BLOCKED_COUNTRIES:-CN}
       - ALLOWED_COUNTRIES=${ALLOWED_COUNTRIES}
+      - CUSTOM_PROXY_MODE=${CUSTOM_PROXY_MODE:-mixed}
+      - SINGBOX_PATH=sing-box
     healthcheck:
-      test: ["CMD", "wget", "-qO-", "http://localhost:7778/"]
+      test: ["CMD-SHELL", "curl -sf http://localhost:7778/ || exit 1"]
       interval: 30s
       timeout: 5s
       retries: 3