build(desktop): point releases at the fork and rebuild the new native module

release.yml already builds and publishes desktop installers for every platform
on a v* tag, so no new workflow was needed — it needed adapting to the fork.

electron-builder published to upstream's repository, so releases (and with them
the electron-updater feed, which had no source at all) went nowhere useful.

More consequential: postinstall ran electron-rebuild against uiohook-napi only.
electron-native-screenshare would have been compiled for Node's ABI rather than
Electron's and failed to load at runtime — and since the loader degrades
quietly by design, the symptom would have been screen sharing with no sound and
no error, which is the exact bug this module exists to fix.

Documented in docs/build-desktop.md, including why the build has to run on
GitHub (Gitea Actions provides no hosted runners, and the module needs MSVC)
and why the Windows runner stays pinned to windows-2022.

packages/desktop/package.json

@@ -18,7 +18,7 @@
     "clean": "rm -rf dist dist-electron",
     "test": "vitest run",
     "test:watch": "vitest",
-    "postinstall": "electron-rebuild -f -w uiohook-napi || node -e \"console.warn('[desktop] uiohook-napi native rebuild skipped - needs build tools (make, g++, python3). Only required to RUN the desktop app; the server, web client, and Docker image are unaffected.')\""
+    "postinstall": "electron-rebuild -f -w uiohook-napi -w electron-native-screenshare || node -e \"console.warn('[desktop] uiohook-napi native rebuild skipped - needs build tools (make, g++, python3). Only required to RUN the desktop app; the server, web client, and Docker image are unaffected.')\""
   },
   "dependencies": {
     "electron-native-screenshare": "^1.2.0",