fix: add repository/author to desktop package.json, use --publish never in CI

electron-builder auto-detects CI and tries to publish to a release,
requiring a repository field and failing when none is found.
- Add repository and author fields to desktop/package.json
- Pass --publish never to electron-builder in the workflow so it builds
  installers without attempting any publish step

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

desktop/package.json

@@ -2,6 +2,8 @@
   "name": "cloudlink-desktop",
   "version": "1.0.0",
   "description": "CloudLink — encrypted messaging and cloud drive",
+  "repository": "https://git.necloud.us/nate/cloudlink",
+  "author": "Nate",
   "main": "main.js",
   "scripts": {
     "start": "electron .",