Package the desktop app for Arch, Debian and Windows

electron-builder produces j621-desktop_*_amd64.deb,
j621-desktop-*.pkg.tar.zst (zstd, lean Arch dependencies instead of the
Electron 2 era default set) and a per-user NSIS installer cross-built with
wine. The launcher entry and Electron's desktopName now agree on
io.j621.desktop so window association works, and package metadata points
at the repository homepage and the non-commercial licence.

desktop/package.json

@@ -4,8 +4,13 @@
   "version": "0.1.0",
   "private": true,
   "description": "Desktop shell for the J621 self-hosted media archive",
-  "author": "JakeBreath",
-  "license": "SEE LICENSE IN ../LICENSE",
+  "author": {
+    "name": "JakeBreath",
+    "email": "tolozacdcmo@gmail.com"
+  },
+  "homepage": "https://gitea.rainbow-herring.ts.net/JakeBreath/J621",
+  "license": "LicenseRef-Jake-Labs-Non-Commercial",
+  "desktopName": "io.j621.desktop",
   "main": "dist/main.js",
   "scripts": {
     "build:main": "tsc -p tsconfig.json",