docs: add Unreleased subsections and update link map for v2.1.0-dusseldorf

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: nanotaboada

CHANGELOG.md

@@ -42,6 +42,14 @@ This project uses famous football stadiums (A-Z) that hosted FIFA World Cup matc
 
 ## [Unreleased]
 
+### Added
+
+### Changed
+
+### Fixed
+
+### Removed
+
 ---
 
 ## [2.1.0 - dusseldorf] - 2026-03-29
@@ -202,7 +210,8 @@ The CD workflow automatically:
 
 ---
 
-[unreleased]: https://github.com/nanotaboada/Dotnet.Samples.AspNetCore.WebApi/compare/v2.0.0-centenario...HEAD
+[unreleased]: https://github.com/nanotaboada/Dotnet.Samples.AspNetCore.WebApi/compare/v2.1.0-dusseldorf...HEAD
+[2.1.0 - dusseldorf]: https://github.com/nanotaboada/Dotnet.Samples.AspNetCore.WebApi/compare/v2.0.0-centenario...v2.1.0-dusseldorf
 [2.0.0 - centenario]: https://github.com/nanotaboada/Dotnet.Samples.AspNetCore.WebApi/compare/v1.1.0-bernabeu...v2.0.0-centenario
 [1.1.0 - bernabeu]: https://github.com/nanotaboada/Dotnet.Samples.AspNetCore.WebApi/compare/v1.0.0-azteca...v1.1.0-bernabeu
 [1.0.0 - azteca]: https://github.com/nanotaboada/Dotnet.Samples.AspNetCore.WebApi/releases/tag/v1.0.0-azteca