feat(org-chart): implement expandable layout and multi-company navigation

Integrate P5-1B through P5-4 shared Core layout, collapse, zoom/pan/fit, company roots and keyboard accessibility. Include React/HTML examples, virtual 20/100/300 employee fixtures, focused checks and the additive data contract.

examples/org-chart/expanded.css

@@ -0,0 +1,9 @@
+* { box-sizing: border-box; }
+body { margin: 0; font-family: 'Noto Sans KR', sans-serif; }
+main { padding: 16px; min-width: 0; }
+h1 { font-size: 22px; }
+.controls, #companies { display: flex; flex-wrap: wrap; align-items: center; gap: 12px; }
+#companies { border: 0; padding: 16px 0; }
+#companies label { display: flex; gap: 8px; align-items: center; }
+#companies legend { padding: 8px 0; }
+button, select { font: inherit; }