chore: Add .claude to .gitignore (a2aproject#311)

So users can experiment with their own CLAUDE.md files, until we have an
official one (if ever)

Author: kabir

.gitignore

@@ -44,3 +44,6 @@ nb-configuration.xml
 # TLS Certificates
 .certs/
 nbproject/
+
+# Private Claude config
+.claude/