chore: swap ko-fi button for markdown GitHub-style variant

Replaces the old CDN image with the official ko-fi githubbutton_sm.svg
rendered via markdown for consistency with the GitHub Sponsors visual.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: erwan-joly

README.md

@@ -17,7 +17,7 @@
 
 ## You like our work ? ##
 <a href='https://github.com/sponsors/0Lucifer0' target='_blank'><img height='48' style='border:0px;height:46px;' src='https://i.gyazo.com/47b2ca2eb6e1ce38d02b04c410e1c82a.png' border='0' alt='Sponsor me!' /></a>
-<a href='https://ko-fi.com/A3562BQV' target='_blank'><img height='46' style='border:0px;height:46px;' src='https://az743702.vo.msecnd.net/cdn/kofi3.png?v=0' border='0' alt='Buy Me a Coffee at ko-fi.com' /></a>
+[![ko-fi](https://ko-fi.com/img/githubbutton_sm.svg)](https://ko-fi.com/A3562BQV)
 <a href='https://www.patreon.com/bePatron?u=6503887' target='_blank'><img height='46' style='border:0px;height:46px;' src='https://c5.patreon.com/external/logo/become_a_patron_button@2x.png' border='0' alt='Become a Patron!' /></a>
 
 ## Warning! ##