fix(changelog): preserve custom release-note sections like "What's New"

[nyaomaru]

Close #86

Summary

Preserve custom release-note sections like "What's New"

Description

• Preserve custom top-level (##) sections from GitHub release notes when generating/updating CHANGELOG.md (including ## What’s New).
• Normalize heading matching for What's Changed / What’s Changed and Full Changelog variants.
• Keep original custom-section order and avoid duplicate section rendering.
• Keep existing What's Changed categorization and Full Changelog link behavior.
• Add tests for section extraction and rendering:
  • tests/utils/release.test.ts
  • tests/utils/llm-output.test.ts

[Copilot]

Pull request overview

Updates the release-notes parsing and changelog rendering pipeline so that custom top-level (##) sections in GitHub Release Notes (e.g., “What’s New”) are preserved in generated/updated CHANGELOG.md, including better handling of typographic heading variants.

Changes:

• Extend parseReleaseNotes to normalize “What’s Changed” / “Full Changelog” heading matching and to preserve custom ## sections (deduped, order preserved).
• Update release-notes fallback generation to proceed when custom sections exist even if no PR items are parsed.
• Add tests covering custom-section extraction/deduplication and rendering when there are no parsed items.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/utils/release.ts	Normalizes heading matching and preserves/dedupes custom ## sections from release notes.
src/utils/llm-output.ts	Allows release-notes-based output when additional sections exist without parsed items.
tests/utils/release.test.ts	Adds coverage for typographic headings and custom-section preservation/deduplication.
tests/utils/llm-output.test.ts	Adds coverage for rendering custom sections when no PR items are parsed.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.