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/views/settings.js

@@ -559,6 +559,31 @@ export async function renderSettings() {
     }
   });
 
+  const stopBtn = h("button", { class: "btn danger" }, "\u23fb " + t("settings.shutdown"));
+  stopBtn.addEventListener("click", async () => {
+    if (!(await confirmDialog(t("settings.shutdownConfirm")))) return;
+    stopBtn.disabled = true;
+    restartBtn.disabled = true;
+    try {
+      await api.shutdown();
+      // the server is gone in ~300ms — replace the app with a static farewell
+      document.body.innerHTML = "";
+      document.body.appendChild(
+        h(
+          "div",
+          { class: "shutdown-screen" },
+          h("div", { class: "shutdown-icon" }, "\u23fb"),
+          h("h2", {}, t("settings.shutdownDone")),
+          h("p", { class: "hint" }, t("settings.shutdownHint"))
+        )
+      );
+    } catch (e) {
+      toast(String(e.message || e), "bad");
+      stopBtn.disabled = false;
+      restartBtn.disabled = false;
+    }
+  });
+
   mount(
     root,
     h(
@@ -682,7 +707,8 @@ export async function renderSettings() {
         h("button", { class: "btn", onClick: () => fileIn.click() }, t("settings.import")),
         fileIn,
         h("div", { class: "grow" }),
-        restartBtn
+        restartBtn,
+        stopBtn
       )
     )
   );