Reset upcoming to released main; add Upcoming Release placeholder

Author: StefanSteiner

website/docs/releases.md

@@ -24,6 +24,8 @@ In case you are wondering why all our releases start with `0.0`, read [this FAQ
 
 :::
 
+###  Upcoming Release
+
 ###  0.0.26479 [September 3 2026]
 * Performance improvements and defect fixes