docs: fix broken star history chart in READMEs and docs
The star history chart in the READMEs and vitepress docs is currently broken because the upstream service no longer works due to GitHub stargazer API restrictions. Switch the chart images to the star-history.dera.page mirror, which uses a different data source that requires no API token, so the chart renders correctly again.
Co-authored-by: SimonFoobar648 <245426116+SimonFoobar648@users.noreply.github.com>
