Persist mesh provider ID across remounts, reject download on Intel Macs

- Store meshProviderId in localStorage so reopening Settings finds the
  previously created provider instead of creating duplicates
- Gate auto-download on process.arch === 'arm64' in addition to darwin
  check, since the bundled binaries are Apple Silicon only

Signed-off-by: jh-block <jhugo@block.xyz>

ui/desktop/src/components/settings/mesh/MeshSettings.tsx

@@ -61,7 +61,13 @@ export const MeshSettings = () => {
   const [saving, setSaving] = useState(false);
   const [error, setError] = useState<string | null>(null);
   const [activeModel, setActiveModel] = useState<string | null>(null);
-  const [meshProviderId, setMeshProviderId] = useState<string>('mesh');
+  const [meshProviderId, setMeshProviderIdState] = useState<string>(
+    () => localStorage.getItem('mesh-provider-id') ?? 'mesh'
+  );
+  const setMeshProviderId = (id: string) => {
+    setMeshProviderIdState(id);
+    localStorage.setItem('mesh-provider-id', id);
+  };
   const [checking, setChecking] = useState(false);
 
   const checkStatus = useCallback(async () => {

ui/desktop/src/main.ts

@@ -1744,7 +1744,7 @@ ipcMain.handle('stop-mesh', async () => {
 });
 
 ipcMain.handle('download-mesh', async () => {
-  if (process.platform !== 'darwin') {
+  if (process.platform !== 'darwin' || process.arch !== 'arm64') {
     return { downloaded: false, error: 'Auto-download is only available on macOS (Apple Silicon)' };
   }