feat(gateway): add scoped proxy egress deployment

.env.example

@@ -2,6 +2,9 @@
 LX_DB_PASSWORD=replace-with-strong-database-password
 LX_JWT_SECRET=replace-with-at-least-32-random-characters
 LX_WEB_PORT=8088
+DEBIAN_MIRROR=https://deb.debian.org/debian
+DEBIAN_SECURITY_MIRROR=https://deb.debian.org/debian-security
+FFMPEG_BINARIES_URL=https://github.com/eugeneware/ffmpeg-static/releases/download
 
 # DeepSeek Anthropic-compatible API
 DEEPSEEK_API_KEY=replace-with-rotated-deepseek-key
@@ -20,6 +23,8 @@ TELEGRAM_WEBHOOK_SECRET=replace-with-random-webhook-secret
 WHATSAPP_GATEWAY_TOKEN=replace-with-at-least-32-random-characters
 WHATSAPP_WEBHOOK_SECRET=replace-with-another-32-random-secret
 WHATSAPP_LOG_LEVEL=info
+# 可选。只影响 WhatsApp 网关出站，不设置系统或平台全局代理。
+WHATSAPP_DEFAULT_PROXY_URL=
 
 PUBLIC_WEBHOOK_BASE_URL=http://host.docker.internal:8088
 APP_PUBLIC_URL=http://127.0.0.1:8088