Docs: point CLAUDE.md to cross-repo Spotless formatting policy

Run `mvn spotless:apply` before every commit that touches .java files.
Canonical policy: workspace/policies/spotless-formatting.md

https://claude.ai/code/session_01Au4VSkHrWmx3FJDYcLSNJo

Author: claude

CLAUDE.md

@@ -750,6 +750,11 @@ See [`../workspace/policies/javadoc-conventions.md`](../workspace/policies/javad
 
 See [`../workspace/policies/spotbugs-suppressions.md`](../workspace/policies/spotbugs-suppressions.md).
 
+## Spotless Formatting
+
+See [`../workspace/policies/spotless-formatting.md`](../workspace/policies/spotless-formatting.md).
+Run `mvn spotless:apply` before every commit that touches `.java` files.
+
 ## jqwik Policy
 
 See [`../workspace/policies/jqwik-prompt-injection.md`](../workspace/policies/jqwik-prompt-injection.md).