fix link in documentation

Signed-off-by: Stefan Bischof <[email protected]>

Author: stbischof

docs/cubeserver/setup/index.md

@@ -4,14 +4,14 @@ This section provides an overview of how to set up and deploy the system in diff
 
 The setup is organized into the following key areas:
 
-## [Probe](./app_probe.md)
+## [Probe](./app.probe.md)
 The right tool for getting to know the OLAP server for development, tutorials, testing and mocking. References tutorials in the [Tutorial](https://daanse.org/cubeserver/tutorial/) folder. 
 
 If you're not sure what to do, choose this one! ✅
 
-## [Pivot](./app_pivot.md)
+## [Pivot](./app.pivot.md)
 Pivot is under construction. It is the foundation for every production Daanse OLAP server.
 
-## [Playground](./app_playground.md)
+## [Playground](./app.playground.md)
 A comprehensive development tool containing all dialects, data sources, web consoles, and helper components for creating and configuring pivot servers. Available only through the git repository due to security considerations.