chore: prepare for next release

CHANGELOG.md

@@ -1,5 +1,7 @@
 # PrivateBin version history
 
+## 2.0.0 (not yet released)
+
 ## 1.7.8 (2025-06-30)
 * FIXED: Duplicate attachment for every comment (#1577)
 * FIXED: Attachments with empty file names (#1577)