ci: add desktop release packaging

[rogerchappel]

Summary

• add Electron Builder packaging config for CrewCmd desktop
• add a Desktop Release GitHub Actions workflow that packages macOS, Windows, and Linux artifacts
• publish a GitHub Release from workflow dispatch or desktop-v* tags with release notes and installer guidance

Verification

• git diff --check
• ruby YAML parse for .github/workflows/desktop-release.yml
• pnpm check in apps/desktop
• pnpm install --frozen-lockfile in apps/desktop
• CSC_IDENTITY_AUTO_DISCOVERY=false pnpm run dist:dir in apps/desktop
• pnpm exec eslint apps/desktop/src/main.cjs apps/desktop/src/preload.cjs
• pnpm lint:check
• pnpm exec tsc --noEmit --pretty false
• push hook: pnpm typecheck && pnpm build

Risk

Medium. This adds release automation, but keeps the first pipeline unsigned and avoids signing/notarization secrets. First GitHub run should be treated as a packaging validation run before announcing a production-grade desktop release.