feat: bootstrap walking skeleton

src/ui/App.tsx

@@ -0,0 +1,27 @@
+import { useEffect } from 'react';
+import { gameRuntime } from '../state/runtime';
+import { ActionPanel } from './ActionPanel';
+import { EventLog } from './EventLog';
+import { ResourceBar } from './ResourceBar';
+
+/**
+ * Walking-skeleton view shell. Boots the runtime once on mount; everything else
+ * renders from the Zustand store the runtime feeds. M1 turns this into a game.
+ */
+export function App() {
+  useEffect(() => {
+    void gameRuntime.boot();
+  }, []);
+
+  return (
+    <main className="mx-auto flex min-h-dvh max-w-2xl flex-col gap-5 px-4 py-8 text-slate-100">
+      <header>
+        <h1 className="font-bold text-2xl tracking-tight">Idlegame</h1>
+        <p className="text-slate-500 text-sm">Walking skeleton — M0 scaffold.</p>
+      </header>
+      <ResourceBar />
+      <ActionPanel />
+      <EventLog />
+    </main>
+  );
+}