feat: scaffold PulseNode dashboard (M1)

Next.js 16 + TypeScript + Tailwind v4 app with a YAML-driven config
system: schema validation (zod), .env interpolation, and a widget
registry rendering bookmark/search/group widgets. CSS custom
properties (--pn-*) drive theming and are overridable from
config.yml's theme.variables. Config load errors surface as a
readable error page instead of crashing the app.

Hot reload, docker/system/http collectors, and the WebSocket push
layer land in later milestones per the approved plan.

app/page.tsx

@@ -0,0 +1,23 @@
+import { configStore, ConfigError } from "@/lib/config/loader";
+import { Dashboard } from "@/components/layout/Dashboard";
+
+export const dynamic = "force-dynamic";
+
+export default function Home() {
+  let config;
+  try {
+    config = configStore.get();
+  } catch (err) {
+    const message = err instanceof ConfigError ? err.message : "Unknown configuration error";
+    return (
+      <main className="mx-auto flex max-w-2xl flex-col gap-4 px-6 py-16">
+        <h1 className="text-lg font-semibold text-status-down">Configuration Error</h1>
+        <pre className="rounded-[var(--radius-widget)] border border-status-down bg-surface p-4 text-sm whitespace-pre-wrap text-fg">
+          {message}
+        </pre>
+      </main>
+    );
+  }
+
+  return <Dashboard config={config} />;
+}