Updated branding assets for dark mode compatibility in docs and README

[patvice]

Summary

• Fixed homepage logo rendering so dark mode reliably uses the white text logo.
• Replaced the embedded GitHub iframe star widget on the docs homepage with a stable badge link.
• Updated README logo rendering to use GitHub theme-specific image fragments for correct light/dark behavior on GitHub.

Why

• The previous setup used prefers-color-scheme for logo selection, which could conflict with the site’s in-page theme toggle.
• The iframe GitHub button rendered poorly in dark mode.
• README needed GitHub-native theme handling so logo colors switch correctly on github.com.