Update startServer JSDoc; surface boot errors via dialog

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

desktop-client/index.js

@@ -67,6 +67,9 @@ app.whenReady().then(async () => {
     },
     onQuit: () => app.quit(),
   });
+}).catch((err) => {
+  dialog.showErrorBox('Failed to start', err && err.message ? err.message : String(err));
+  app.exit(1);
 });
 
 app.on('window-all-closed', () => {

desktop-client/server.js

@@ -9,7 +9,7 @@ const { initialState, mergeState } = require('./state');
  * @param {Object} opts
  * @param {number} opts.port         Port to listen on (e.g. 9095).
  * @param {string} [opts.overlayDir] Absolute path to the overlay/ directory to serve as static files. Optional (omit for tests).
- * @returns {Promise<{ setState: (update: object) => object, stop: () => Promise<void> }>}
+ * @returns {Promise<{ setState: (update: object) => object, stop: () => Promise<void>, port: number }>}
  */
 async function startServer({ port, overlayDir }) {
   let currentState = { ...initialState };