feat(admin): power controls — stop everything & power off, restart everything

Settings gains a second service button next to restart: stop every managed
local model server and exit the gateway process (nothing is respawned; in
Docker the restart policy decides). The SPA replaces itself with a static
"gateway is off" screen since the API is gone. The restart button is
relabeled "Restart everything" to say what it always did — the gateway
re-execs itself and managed servers come back with it. Translated in all
seven languages.

web/js/i18n/zh.js

@@ -536,9 +536,13 @@ export default {
   "keys.snip.withKey": "下面的示例已包含你刚创建的密钥。",
   "keys.snip.openMode": "未配置 API 密钥 — 网关接受任意密钥值。",
   "keys.snip.keyPh": "你的 API 密钥",
-  "settings.restart": "重启网关",
-  "settings.restartConfirm": "重启网关？进行中的请求会中断；本地模型服务器也会重启。",
+  "settings.restart": "全部重启",
+  "settings.restartConfirm": "重启网关和所有本地模型服务器？正在处理的请求将被中断。",
   "settings.restarting": "正在重启 — 网关恢复后页面会自动刷新……",
+  "settings.shutdown": "全部停止并关机",
+  "settings.shutdownConfirm": "停止所有本地模型服务器并关闭网关？在你重新启动网关之前，API 和此面板都将无法响应。",
+  "settings.shutdownDone": "网关已关闭。",
+  "settings.shutdownHint": "所有本地模型服务器已停止，进程已退出。请在服务器上重新启动网关以恢复面板。",
   "bench.title": "本地模型速度",
   "bench.hint": "在本机运行 `cortiq bench` — 真实 tok/s，一次一个模型。",
   "bench.run": "测速",