feat(FN-1070): restore desktop Electron scaffolding

- Reintroduce the @fusion/desktop workspace package with Electron main, preload, and renderer entrypoints
- Add desktop build/test tooling (TypeScript, Vitest, electron-builder) and update workspace build dependency settings for Electron
- Wire secure IPC bridge APIs for app version/quit flows with exported preload typings
- Add README usage docs and unit tests covering main-process window/tray behavior and preload API wiring

package.json

@@ -23,6 +23,7 @@
   },
   "pnpm": {
     "onlyBuiltDependencies": [
+      "electron",
       "esbuild",
       "koffi",
       "protobufjs"