docs: add retrospective CHANGELOG.md and link in README

[Avonaxe]

Description

Adds a retrospective CHANGELOG.md at the repository root based on historical GitHub release notes, formatted according to Keep a Changelog standards. Also adds a link to the changelog in the central navigation menu of the README.md.

Type of Change

• Skill Proposal: New Skill (Contains manifest.yaml, skill.py, and instructions.md)
• Bug Report Fix: Non-breaking change which fixes an execution error or framework bug
• Doc Fix: Documentation Update
• Framework Feature / RFC Updates: Core Framework Update (Changes to base_skill.py, loader.py, etc.)

Checklist (all PRs)

• My code follows the Agent Code of Conduct.
• I have run python -m flake8 . and pytest tests/ locally (or the subset relevant to this change).

New or updated skill (complete only if this PR adds or changes a skill under skills/)

Skipped: Documentation-only PR

Constitution & Safety (if adding or modifying a skill)

Skipped: Documentation-only PR

Related Issues

Closes #91

[rosspeili]

Thanks @Avonaxe, this is a strong first pass and closes the intent of #91. The retrospective coverage from v0.2.0–v0.2.9 is thorough and the README nav link is exactly what we wanted.

Approve with minor revisions before merge:

1. [Unreleased], Please rebase on latest main and add entries for work since v0.2.9, at minimum:

   • feat: migrate from google-generativeai to google-genai SDK #97 — migrate framework/examples from google-generativeai to google-genai
   • docs: improve README navigation and skill catalog discoverability #98 / docs: update Gemini snippets to google-genai #92 — README navigation and Gemini doc snippet updates
   • Any other user-facing merges landed after the 0.2.9 bump

2. Keep a Changelog, Remove empty ### Fixed / ### Removed sections that only contain (None). KaC guidance says not to include empty sections.

3. Optional polish (nice to have):

   • Add the SemVer adherence line under the KaC header
   • Quick pass for hidden/special Unicode characters (GitHub flagged the file)
   • One sentence in CONTRIBUTING: “Add user-facing changes to CHANGELOG.md under [Unreleased]; finalize the section when cutting a release”

Manual maintenance is intentional for v1 (per #91), no automation required in this PR.

Happy to merge once 1–2 are addressed. Nice work on the retrospective dig through release history.

[Avonaxe]

Thanks for the information, will work on it