[Phase 3] Update library README and package metadata

[afucher]

Update the library's main README.md and package.json to reflect the new documentation site.

Deliverable

The library's public-facing documentation entry points are all up to date and point to the new site.

Acceptance Criteria

• README.md updated:

  • Link to new docs site updated to https://astrodraw.github.io/
  • Brief description of what's in the new docs
  • Removed or archived old "in progress" notice
  • Screenshot of new docs site added (optional but nice)

• package.json reviewed:

  • homepage field already set to https://astrodraw.github.io/ (verify)
  • repository field correct
  • bugs URL points to GitHub issues

• Contributing guide updated (if separate file exists):

  • Points to /docs/contributing in the new docs site

• CHANGELOG.md created or updated:

  • Starting point: v3.0.2
  • Follows Keep a Changelog format
  • Matches what's in the docs site changelog

• Release process documentation updated:

  • Explains how to update changelog when releasing new version
  • Explains SinceBadge usage for new features

Related Plan Section

docs-plan.md §5 (New Features & Changelog Strategy)