feat: apply imported design (bento grid, real elevation tokens, live indicator)

Imports the visual direction from a claude.ai/design session ("PulseNode
Dashboard.dc.html") and reconciles it with the app's existing choices
rather than a wholesale swap: kept the IBM Plex Sans/Mono + Space
Grotesk typography and the pulse-green accent concept from the earlier
pass, adopted the imported design's structural ideas - a real
tonal/elevation token system (derived divider/muted colors via
color-mix instead of hardcoded per-theme duplicates, actual box-shadow
elevation), a 12-column bento grid with per-widget-type column spans
instead of uniform equal-width cards, fading-edge section dividers,
and a shared WidgetCard/MetricBar/StatusTag vocabulary so every widget
type stops repeating its own card markup.

Icons come from @phosphor-icons/react's /ssr entrypoint (bundled at
build time) rather than the imported design's unpkg.com CDN script -
that script is fine for the standalone design-tool preview, but a
runtime third-party call would break the self-hosted-only principle
already established (fonts self-hosted via next/font, no external
requests). New app/icon.svg reuses the same nav badge mark as the
favicon, replacing the never-touched create-next-app default.

Two new pieces of real functionality prompted by the design's mockup
toast/live-indicator, not just decoration: a "live" WebSocket
connection-status indicator (lib/ws/client.ts now tracks and exposes
real connection state), and a toast that fires on actual config:update
and config:error events - the latter finally surfaces config validation
failures in the browser, previously visible only in server logs despite
being designed for exactly this back in M1.

components/layout/Toast.tsx

@@ -0,0 +1,28 @@
+"use client";
+
+import { CheckCircle, WarningCircle } from "@phosphor-icons/react/ssr";
+import { useConfigToasts } from "@/lib/ws/client";
+
+export function ToastStack() {
+  const toasts = useConfigToasts();
+
+  if (toasts.length === 0) return null;
+
+  return (
+    <div className="fixed right-6 bottom-6 z-50 flex flex-col gap-2">
+      {toasts.map((toast) => (
+        <div
+          key={toast.id}
+          className="pn-toast flex max-w-[340px] items-center gap-2.5 rounded-lg border border-border bg-surface px-3.5 py-3 shadow-[var(--pn-shadow-md)]"
+        >
+          {toast.tone === "ok" ? (
+            <CheckCircle size={20} className="shrink-0 text-accent" aria-hidden />
+          ) : (
+            <WarningCircle size={20} className="shrink-0 text-status-down" aria-hidden />
+          )}
+          <span className="text-[13px] text-fg">{toast.message}</span>
+        </div>
+      ))}
+    </div>
+  );
+}