feat(energy): add module shell, register in nav

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/modules/energy/HydrogenView.tsx

@@ -0,0 +1,7 @@
+export default function HydrogenView() {
+  return (
+    <div className="bg-white rounded-2xl border border-slate-100 shadow-sm p-6 text-center text-slate-400 text-sm">
+      氢能视图占位 — 将在 Task 3-5 实现
+    </div>
+  );
+}