docs: update changelog for sessions_spawn thinking

CHANGELOG.md

@@ -2,6 +2,11 @@
 
 Docs: https://docs.clawd.bot
 
+## 2026.1.18-1
+
+### Changes
+- Tools: allow `sessions_spawn` to override thinking level for sub-agent runs.
+
 ## 2026.1.17-3
 
 ### Changes