docs(readme): add Ko-fi to the donations buttons, fix Sponsors label

The single donation button used a 'Buy Me A Coffee' image that actually
linked to GitHub Sponsors. Split it into two correctly labeled badges:
GitHub Sponsors and Ko-fi (ko-fi.com/4gray, same as the blog).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -187,7 +187,8 @@ the host `mpv` executable to the embedded backend by default.
 
 [![Get it from the Snap Store](https://snapcraft.io/static/images/badges/en/snap-store-black.svg)](https://snapcraft.io/iptvnator)
 
-<a href="https://github.com/sponsors/4gray" target="_blank"><img src="https://cdn.buymeacoffee.com/buttons/default-green.png" alt="Buy Me A Coffee" width="185"></a>
+<a href="https://github.com/sponsors/4gray" target="_blank"><img src="https://img.shields.io/badge/GitHub%20Sponsors-EA4AAA?style=for-the-badge&logo=githubsponsors&logoColor=white" alt="Sponsor on GitHub"></a>
+<a href="https://ko-fi.com/4gray" target="_blank"><img src="https://img.shields.io/badge/Ko--fi-FF5E5B?style=for-the-badge&logo=ko-fi&logoColor=white" alt="Support on Ko-fi"></a>
 
 ## Troubleshooting