docs: unify markdown files with documentation titles

This is preparational work to reduce the surface are of the different mappings

We want to reduce the following:

/guides/secrets.md -> Guides/getting started/How to use flakes with sops -> with '# Secrets Management'

- Title
- URI
- Filepath

should follow a stricter pattern to make it easy to maintain

docs/site/guides/nixos-rebuild.md

@@ -64,5 +64,5 @@ nixos-rebuild switch --flake .#my-machine --target-host root@target-ip --build-h
 
 ## Related Documentation
 
-- [Update Your Machines](getting-started/update.md) - Using clan's update command
-- [Variables (Vars)](vars/vars-overview.md) - Understanding the vars system
+- [Update Your Machines](/guides/getting-started/update-machine.md) - Using clan's update command
+- [Variables (Vars)](/guides/vars/vars-overview.md) - Understanding the vars system