feat(orgchart): integrate chart-only viewport and scoped guard fixes

Add initial fit and direct wheel zoom with preserved default presentation. Integrate five scoped GuardFix findings and AI generation preselection policy. Exclude Cell experiments and retain five historical guard failures.

examples/org-chart-chart-only/chart-only.css

@@ -0,0 +1,6 @@
+/* Page layout only: the chart canvas fills the window. */
+html, body { height: 100%; margin: 0; background: #ffffff; }
+#chart { height: 100%; }
+/* Verification only: page content above and below a bounded canvas. */
+body.embed { height: auto; }
+body.embed #chart { height: 480px; margin: 600px 0 1400px; }