release: make future notes creator-first

[FernandoAbishai]

Summary

• Add a creator-first Download -> Install -> What's new hierarchy to future generated release notes.
• Build the primary download link from manifest.releaseTag and manifest.artifact.filename.
• Preserve platform, alpha, signing, model, checksum, attestation, and bounded provenance truth.
• Strengthen release-note smoke coverage for order, exact URL, changelog selection, dry-run labeling, and verification commands.

Release impact

• Release-system behavior: changed only generated release-note presentation.
• Installer/DMG, signing/notarization, runtime/backend/frontend, and public six-file bundle shape: unchanged.
• No release, tag, workflow dispatch, or published v0.1.0-alpha.5 mutation.

Verification

• npm run smoke:release-notes
• npm run smoke:public-release
• npm run smoke:release-identity
• npm run smoke:release-metadata
• npm run smoke:release-workflow
• npm run smoke:published-release
• npm run lint
• node --check scripts/prepare-public-release.js scripts/smoke-release-notes.js
• git diff --check

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