docs: add nixos-rebuild-test usage to CLAUDE.md

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CLAUDE.md

@@ -35,6 +35,21 @@ nix build .#create-host
 
 Do not automatically deploy changes. Deployments are usually done by updating the master branch, and then triggering the auto update on the specific host.
 
+### Testing Feature Branches on Hosts
+
+All hosts have the `nixos-rebuild-test` helper script for testing feature branches before merging:
+
+```bash
+# On the target host, test a feature branch
+nixos-rebuild-test boot <branch-name>
+nixos-rebuild-test switch <branch-name>
+
+# Additional arguments are passed through to nixos-rebuild
+nixos-rebuild-test boot my-feature --show-trace
+```
+
+When working on a feature branch that requires testing on a live host, suggest using this command instead of the full flake URL syntax.
+
 ### Flake Management
 
 ```bash