ci: add a fast Windows-only desktop build

release.yml builds four platforms and publishes a release, which is right for a
release and slow for 'give me an exe to test'. Wall time is set by the Windows
job, which compiles native modules and downloads Electron twice because it
targets x64 and arm64 together — and Windows-on-ARM is not something this group
runs.

This path builds one architecture, caches the Electron and electron-builder
downloads (~100MB re-fetched every run otherwise), and uploads the installer as
an artifact, so it needs neither a tag nor a version bump.

Kept as a separate file: release.yml comes from upstream and takes merges, so
editing it would conflict on every update.

Cost matters too on a private repository: macOS runners bill at 10x and Windows
at 2x, so the full matrix was paying for macOS builds on every tag.

.github/workflows/build-windows.yml

@@ -0,0 +1,81 @@
+# Caminho rápido: só Windows x64, disparado à mão.
+#
+# O `release.yml` continua sendo o release de verdade (todas as plataformas,
+# publica release e alimenta o electron-updater). Este aqui existe para quando
+# você só quer um .exe para testar, sem marcar versão.
+#
+# Arquivo separado de propósito: o release.yml veio do upstream e recebe merges;
+# mexer nele criaria conflito a cada atualização.
+name: Build Windows (rápido)
+
+on:
+  workflow_dispatch:
+    inputs:
+      arch:
+        description: Arquitetura
+        required: false
+        default: x64
+        type: choice
+        options: [x64, arm64]
+
+permissions:
+  contents: read
+
+jobs:
+  build:
+    # windows-2022, não windows-latest: a imagem latest traz o Visual Studio 18,
+    # que o node-gyp embutido no electron-rebuild não detecta ao compilar os
+    # módulos nativos. Mesma razão documentada no release.yml.
+    runs-on: windows-2022
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd # v5.0.1
+
+      - name: Setup pnpm
+        uses: pnpm/action-setup@fc06bc1257f339d1d5d8b3a19a8cae5388b55320 # v5.0.0
+        with:
+          version: 10.34.3
+
+      - name: Setup Node.js
+        uses: actions/setup-node@a0853c24544627f65ddf259abe73b1d18a591444 # v5.0.0
+        with:
+          node-version: 20
+          cache: pnpm
+
+      # ~100MB de binários do Electron e das ferramentas do NSIS, baixados a
+      # cada execução sem isto. É o maior ganho depois de cortar o arm64.
+      - name: Cache Electron binaries
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~\AppData\Local\electron\Cache
+            ~\AppData\Local\electron-builder\Cache
+          key: electron-cache-${{ runner.os }}-${{ hashFiles('**/pnpm-lock.yaml') }}
+          restore-keys: electron-cache-${{ runner.os }}-
+
+      - name: Install dependencies
+        run: pnpm install --frozen-lockfile
+
+      - name: Build shared package
+        run: pnpm --filter @backspace/shared build
+
+      - name: Compile desktop TypeScript
+        working-directory: packages/desktop
+        run: pnpm exec tsc
+
+      # --publish never: sem release, sem precisar de tag nem bump de versão.
+      # O instalador sai como artefato desta execução.
+      - name: Build installer
+        working-directory: packages/desktop
+        run: pnpm exec electron-builder --win --${{ inputs.arch || 'x64' }} --publish never
+        env:
+          CSC_IDENTITY_AUTO_DISCOVERY: "false"
+
+      - name: Upload installer
+        uses: actions/upload-artifact@v4
+        with:
+          name: backspace-windows-${{ inputs.arch || 'x64' }}
+          path: packages/desktop/dist-electron/*.exe
+          retention-days: 14
+          if-no-files-found: error