Fix CHANGELOG for v16.2.0.beta.13 release

- Restore [Unreleased] section header for future changes
- Fix v16.2.0.beta.13 diff link to compare from 16.1.1 (last stable)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: justin808

CHANGELOG.md

@@ -19,6 +19,8 @@ After a release, please make sure to run `bundle exec rake update_changelog`. Th
 
 ## Versions
 
+### [Unreleased]
+
 ### [v16.2.0.beta.13] - 2025-12-07
 
 Changes since the last non-beta release.
@@ -1857,7 +1859,7 @@ such as:
 - Fix several generator-related issues.
 
 [unreleased]: https://github.com/shakacode/react_on_rails/compare/v16.2.0.beta.13...master
-[v16.2.0.beta.13]: https://github.com/shakacode/react_on_rails/compare/v16.2.0.beta.11...v16.2.0.beta.13
+[v16.2.0.beta.13]: https://github.com/shakacode/react_on_rails/compare/16.1.1...v16.2.0.beta.13
 [v16.2.0.beta.11]: https://github.com/shakacode/react_on_rails/compare/16.1.1...v16.2.0.beta.11
 [16.1.1]: https://github.com/shakacode/react_on_rails/compare/16.1.0...16.1.1
 [16.1.0]: https://github.com/shakacode/react_on_rails/compare/16.0.0...16.1.0