* docs: add Changelog tab and clean up overview page
- Remove v0.5.0 release banner and stats grid from docs/index.md
- Add Changelog navigation tab to docs/docs.json after FAQ
- Create docs/changelog.md sourced from CHANGELOG.md with full Mintlify
formatting: one accordion per release (Unreleased → v0.0.1), icons,
pip install snippets, Added/Fixed/Security sub-sections, and a change
type legend
* docs: fix broken index#whats-new link in quickstart — point to changelog