Add macOS DMG integration tests

[jozefizso]

Summary

Adds the macOS integration workflow for the Node 24 appdmg packages.

• adds npm run test:integration for real DMG-generation tests
• creates, mounts, inspects, and detaches generated DMGs on macOS
• covers modern JSON, legacy JSON, custom names, explicit image format, mounted volume, app bundle, document file, /Applications symlink, background assets, .VolumeIcon.icns, and .DS_Store
• keeps npm test as the fast unit suite
• adds a dedicated macOS integration CI job after the appdmg and CLI unit jobs
• hardens the hdiutil attach mount parser for volume names containing spaces
• keeps screenshot/capture-window comparison out of the default test path

Verification

• npm test
• npm run test:integration
• npm audit --audit-level=moderate
• npm ls --omit=dev --all
• npm pack --dry-run
• node --check ... for library sources and tests
• npm ci && npm test && npm audit --audit-level=moderate && npm ls --omit=dev --all && npm pack --dry-run && node --check ... in packages/cli
• workflow YAML parse

Closes #8

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Retry hdiutil detach in integration cleanup

The integration helper does a single hdiutil detach attempt, but macOS often returns transient Resource busy (exit code 16) immediately after file reads; this repo’s production detach path already handles that with retries (lib/darwin/hdiutil.js). In CI, a transient busy mount will make these integration tests fail even when DMG generation is correct, so cleanup should mirror the retry/backoff behavior to avoid flaky failures.

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