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.

.github/workflows/build-windows.yml

@@ -60,6 +60,22 @@ jobs:
       - name: Build shared package
         run: pnpm --filter @backspace/shared build
 
+      # O postinstall termina em `|| console.warn` para que quem não tem
+      # ferramentas de build consiga instalar. No CI isso transforma falha em
+      # sucesso silencioso: o instalador sai sem o módulo nativo e o app
+      # compartilha tela sem som, sem erro nenhum. Então verifica-se o
+      # resultado em vez de confiar no código de saída.
+      - name: Verify native audio module compiled
+        shell: bash
+        run: |
+          found=$(find node_modules/.pnpm -path '*electron-native-screenshare*' -name '*.node' 2>/dev/null | head -5)
+          if [ -z "$found" ]; then
+            echo "::error::electron-native-screenshare has no compiled .node — the installer would ship without system-audio capture"
+            find node_modules/.pnpm -maxdepth 1 -name 'electron-native-screenshare*' -printf '%p\n' 2>/dev/null || true
+            exit 1
+          fi
+          echo "OK:"; echo "$found"
+
       - name: Compile desktop TypeScript
         working-directory: packages/desktop
         run: pnpm exec tsc