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.html

@@ -0,0 +1,6 @@
+<!doctype html>
+<html lang="ko"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width,initial-scale=1"><link rel="icon" href="data:,"><title>확장형 조직도 · 가상 데이터</title>
+<link rel="stylesheet" href="./assets/hm-theme.css"><link rel="stylesheet" href="./expanded.css"></head>
+<body><main><h1>확장형 조직도 · HTML Core 예시</h1><p>모든 직원은 고정된 가상 데이터입니다.</p>
+<div class="controls"><label for="dataset">가상 데이터</label><select id="dataset"><option value="small">Small · 20명</option><option value="medium">Medium · 100명</option><option value="large">Large · 300명</option></select><button id="all" type="button">전체 회사</button><button id="none" type="button">선택 해제</button></div>
+<fieldset id="companies"><legend>표시할 회사 · 복수 선택 가능</legend></fieldset><div id="chart"></div><p id="error" role="alert"></p></main><script type="module" src="./expanded-app.js"></script></body></html>