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.

packages/org-chart-react/src/OrgChart.tsx

@@ -20,6 +20,10 @@ export function OrgChart({
   displayMode,
   layoutMode,
   companyId,
+  selectedCompanyIds,
+  companyTopNodes,
+  employeeConnections,
+  zoom,
   organizationLinks,
   onEmployeeClick,
   className,
@@ -66,6 +70,10 @@ export function OrgChart({
         displayMode,
         layoutMode,
         companyId,
+        selectedCompanyIds,
+        companyTopNodes,
+        employeeConnections,
+        zoom,
         organizationLinks,
         onEmployeeClick: hasEmployeeCallback ? (employee, context) => {
           if (generationRef.current === generation) committedRef.current.onEmployeeClick?.(employee, context);
@@ -105,7 +113,17 @@ export function OrgChart({
         }
       }
     };
-  }, [aggregationPolicy, engineStylesheetUrl, coreStylesheetUrl, displayMode, layoutMode, companyId, organizationLinks, hasEmployeeCallback]);
+  }, [aggregationPolicy, engineStylesheetUrl, coreStylesheetUrl, displayMode, layoutMode, companyId, companyTopNodes, employeeConnections, zoom, organizationLinks, hasEmployeeCallback]);
+
+  useLayoutEffect(() => {
+    const instance = instanceRef.current;
+    if (!instance || layoutMode !== 'auto') return;
+    void instance.handle.setSelectedCompanies(selectedCompanyIds).catch(error => {
+      if (instanceRef.current !== instance) return;
+      try { committedRef.current.onLifecycleError?.(error); }
+      catch { /* Match other lifecycle callbacks: never leak a rejected Promise. */ }
+    });
+  }, [selectedCompanyIds, layoutMode]);
 
   useLayoutEffect(() => {
     const instance = instanceRef.current;