feat: replace panel proxy URL with outbound-based egress bridge

Instead of requiring a manual SOCKS5/HTTP URL, the panel now lets the
admin pick an Xray outbound from a dropdown (same UX as Geodata
Auto-Update). At runtime, injectPanelEgress appends a loopback SOCKS
inbound (tag: panel-egress) and prepends a routing rule so the panel's
own HTTP traffic — version checks, Telegram, normal geo-file updates —
is routed through the chosen outbound. Xray-native Geodata Auto-Update
is unaffected (it uses its own geodata.outbound inside Xray). Blackhole
outbounds are excluded from both picker dropdowns since routing any
download through one just drops it. Translations updated for all 13
locales.

internal/web/translation/zh-CN.json

@@ -938,8 +938,9 @@
       "panelUrlPathDesc": "必须以 '/' 开头，以 '/' 结尾",
       "pageSize": "分页大小",
       "pageSizeDesc": "定义入站表的页面大小。设置 0 表示禁用",
-      "panelProxy": "面板网络代理",
-      "panelProxyDesc": "通过此代理路由面板自身的出站请求(geo 更新、Xray/面板版本检查、Telegram),以绕过服务端对 GitHub/Telegram 的过滤。接受 socks5:// 或 http(s)://,如本地 Xray SOCKS 入站。留空表示直连。",
+      "panelOutbound": "面板流量出站",
+      "panelOutboundDesc": "通过此 Xray 出站路由面板自身的请求(面板/Xray 版本检查与下载、Telegram、普通 geo 文件更新),以绕过服务端对 GitHub/Telegram 的过滤。本地桥接入站会自动添加到运行中的配置并实时生效。Xray 原生的 Geodata 自动更新不受影响,它有自己的下载出站。留空表示直连。",
+      "panelOutboundPh": "直连",
       "remarkModel": "备注模型和分隔符",
       "datepicker": "日期选择器",
       "datepickerPlaceholder": "选择日期",