feat(desktop): add Contact/Report/Discord links to Help menu

The desktop Help menu only exposed a repo link and Export
Diagnostics. The web entry rail already gives users one-click
access to docs, issues, and Discord; the packaged desktop app
had no equivalent, so users in the standalone client had no
in-app path to report a bug or reach the community.

Expand the Help submenu to mirror those affordances:
Documentation, Contact Us, Report Issue, and Join Discord, all
opening the canonical URLs already used by the web help menu
and README. Tag the submenu role: "help" so macOS treats it as
the standard Help menu.

apps/desktop/src/main/index.ts

@@ -236,11 +236,31 @@ function installDesktopMenu(
       },
       {
         label: "Help",
+        role: "help",
         submenu: [
           {
-            label: "Open Design",
+            label: "Documentation",
             click() {
-              void shell.openExternal("https://github.com/nexu-io/open-design");
+              void shell.openExternal("https://github.com/nexu-io/open-design#readme");
+            },
+          },
+          { type: "separator" },
+          {
+            label: "Contact Us",
+            click() {
+              void shell.openExternal("https://x.com/nexudotio");
+            },
+          },
+          {
+            label: "Report Issue",
+            click() {
+              void shell.openExternal("https://github.com/nexu-io/open-design/issues/new");
+            },
+          },
+          {
+            label: "Join Discord",
+            click() {
+              void shell.openExternal("https://discord.gg/mHAjSMV6gz");
             },
           },
           { type: "separator" },