feat(org-chart): support external CSS themes and align documentation

examples/org-chart-react/p11.html

@@ -0,0 +1,2 @@
+<!doctype html>
+<html lang="ko"><meta charset="utf-8"><meta name="viewport" content="width=device-width,initial-scale=1"><link rel="icon" href="data:,"><title>OrgChart P11 theme verification</title><body><main id="root"></main><script type="module" src="./p11.tsx"></script></body></html>