Remove committed banner image from README, keep adserver banners (#293)

Removes the committed `fishjam-card.png` header from the README so the
banner is served exclusively via the swm-delivery adserver links.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: czerwiukk

README.md

@@ -1,8 +1,6 @@
-<img src="./.github/images/fishjam-card.png" width="100%">
-
-[![Ad](https://swm-delivery.com/www/images/zone-gh-fishjam-1?n=1)](https://swm-delivery.com/www/delivery/ck.php?zoneid=zone-gh-fishjam-1&n=1)
-[![Ad](https://swm-delivery.com/www/images/zone-gh-fishjam-2?n=1)](https://swm-delivery.com/www/delivery/ck.php?zoneid=zone-gh-fishjam-2&n=1)
-[![Ad](https://swm-delivery.com/www/images/zone-gh-fishjam-3?n=1)](https://swm-delivery.com/www/delivery/ck.php?zoneid=zone-gh-fishjam-3&n=1)
+[![Ad](https://swm-delivery.com/www/images/zone-gh-fishjam-1?n=2)](https://swm-delivery.com/www/delivery/ck.php?zoneid=zone-gh-fishjam-1&n=2)
+[![Ad](https://swm-delivery.com/www/images/zone-gh-fishjam-2?n=2)](https://swm-delivery.com/www/delivery/ck.php?zoneid=zone-gh-fishjam-2&n=2)
+[![Ad](https://swm-delivery.com/www/images/zone-gh-fishjam-3?n=2)](https://swm-delivery.com/www/delivery/ck.php?zoneid=zone-gh-fishjam-3&n=2)
 
 # Fishjam Server SDK