docs: add changelog entry for thinkingLevel/thinkingBudget

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: brendan-kellam

CHANGELOG.md

@@ -7,6 +7,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+- Added `thinkingLevel` and `thinkingBudget` configuration options for Google Generative AI and Google Vertex providers. [#1110](https://github.com/sourcebot-dev/sourcebot/pull/1110)
+
+### Changed
+- Deprecated `GOOGLE_VERTEX_THINKING_BUDGET_TOKENS` environment variable in favor of per-model `thinkingBudget` config. [#1110](https://github.com/sourcebot-dev/sourcebot/pull/1110)
+
 ## [4.16.8] - 2026-04-09
 
 ### Added