fix(desktop): expose About and Check for Updates in Help menu on Windows/Linux (#888)

On macOS these items live in the application menu by platform convention,
but Windows and Linux have no app menu, leaving users with no way to
view the version or trigger an update check. Add them to the Help menu
on non-darwin platforms.

Refs #784

Author: lefarcen

apps/desktop/main/index.ts

@@ -505,6 +505,27 @@ function triggerUpdateCheck(): void {
   });
 }
 
+function showAboutDialog(): void {
+  const version = app.getVersion();
+  const detailLines = [
+    `Version ${version}`,
+    `Electron ${process.versions.electron}`,
+    `Chromium ${process.versions.chrome}`,
+    `Node ${process.versions.node}`,
+  ];
+  const options = {
+    type: "info" as const,
+    title: "About Nexu",
+    message: "Nexu",
+    detail: detailLines.join("\n"),
+    buttons: ["OK"],
+    noLink: true,
+  };
+  void (mainWindow
+    ? dialog.showMessageBox(mainWindow, options)
+    : dialog.showMessageBox(options));
+}
+
 function installApplicationMenu(): void {
   const developMenu: MenuItemConstructorOptions = {
     label: "Develop",
@@ -542,20 +563,42 @@ function installApplicationMenu(): void {
     ],
   };
 
-  const helpMenu: MenuItemConstructorOptions = {
-    role: "help",
-    submenu: [
+  const helpSubmenu: MenuItemConstructorOptions[] = [
+    {
+      label: "Export Diagnostics…",
+      click: () => {
+        void exportDiagnostics({
+          orchestrator,
+          runtimeConfig,
+          source: "help-menu",
+        }).catch(() => undefined);
+      },
+    },
+  ];
+
+  // On macOS About/Check-for-Updates live in the application menu by
+  // platform convention. On Windows/Linux there is no app menu, so surface
+  // them in Help instead (issue nexu-io/nexu#784).
+  if (process.platform !== "darwin") {
+    helpSubmenu.push(
+      { type: "separator" },
       {
-        label: "Export Diagnostics…",
-        click: () => {
-          void exportDiagnostics({
-            orchestrator,
-            runtimeConfig,
-            source: "help-menu",
-          }).catch(() => undefined);
-        },
+        id: "check-for-updates",
+        label: "Check for Updates…",
+        enabled: app.isPackaged && runtimeConfig.updates.autoUpdateEnabled,
+        click: () => triggerUpdateCheck(),
       },
-    ],
+      {
+        id: "about-nexu",
+        label: `About Nexu (v${app.getVersion()})`,
+        click: () => showAboutDialog(),
+      },
+    );
+  }
+
+  const helpMenu: MenuItemConstructorOptions = {
+    role: "help",
+    submenu: helpSubmenu,
   };
 
   const template: MenuItemConstructorOptions[] = [