Split desktop draft release and asset publishing

[h4yfans]

Summary

• create draft desktop releases automatically on pushes to main using Release Drafter
• build and upload desktop assets only after a draft release is published
• derive the desktop app version from the published release tag before packaging

Verification

• node --test scripts/desktop-release-metadata.test.mjs
• node scripts/desktop-release-metadata.mjs --from-tag --tag v2026.4.27-002
• ruby -e "require 'yaml'; Dir['.github/workflows/*.yml'].each { |f| YAML.load_file(f) }; YAML.load_file('.github/release-drafter.yml'); puts 'yaml-ok'"\n- pnpm exec prettier --check .github/workflows/desktop-draft-release.yml .github/workflows/release.yml scripts/desktop-release-metadata.mjs scripts/desktop-release-metadata.test.mjs\n- git diff --check -- .github/workflows/desktop-draft-release.yml .github/workflows/release.yml scripts/desktop-release-metadata.mjs scripts/desktop-release-metadata.test.mjs