fix(ci): actually compile the native audio module, and prove it

The previous run went green and produced an installer with no system-audio
capture in it — the exact silent failure this module exists to prevent.

Two causes. electron-rebuild takes -w as one comma-separated list, not a
repeated flag; passing it twice made argv.w an array and the CLI threw
'argv.w.split is not a function', which also broke uiohook-napi's rebuild that
had been working. And pnpm 10 refuses to run a dependency's build script unless
it is listed in onlyBuiltDependencies, so node-gyp never ran for it at all —
the log said 'Ignored build scripts' and nothing else complained.

Neither surfaced because desktop's postinstall ends in , which
exists so contributors without build tools can install. That is reasonable
locally and dangerous in CI, so the workflow now asserts a compiled .node
exists and fails loudly when it does not, instead of trusting an exit code that
was designed to lie.

package.json

@@ -2,7 +2,7 @@
   "name": "backspace",
   "version": "1.1.0",
   "private": true,
-  "description": "Open, self-hosted communication platform — text, voice, video, and federation",
+  "description": "Open, self-hosted communication platform \u2014 text, voice, video, and federation",
   "license": "AGPL-3.0-only",
   "author": "Jannis Braun",
   "homepage": "https://github.com/TheZwiss/backspace",
@@ -32,8 +32,9 @@
   "pnpm": {
     "onlyBuiltDependencies": [
       "better-sqlite3",
-      "esbuild",
       "electron",
+      "electron-native-screenshare",
+      "esbuild",
       "sharp"
     ],
     "patchedDependencies": {