Clarify reserved DOI citation status

CITATION.cff

@@ -26,4 +26,4 @@ preferred-citation:
   year: 2026
   doi: "10.5281/zenodo.21781711"
   url: "https://doi.org/10.5281/zenodo.21781711"
-  notes: "Preprint archived on Zenodo."
+  notes: "Preprint prepared for archival on Zenodo under the reserved DOI."