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/widgets/StatusTag.tsx

@@ -0,0 +1,14 @@
+export function StatusTag({ children, tone = "accent" }: { children: React.ReactNode; tone?: "accent" | "down" | "degraded" | "neutral" }) {
+  const toneClass = {
+    accent: "bg-accent/15 text-accent border-accent/40",
+    down: "bg-status-down/15 text-status-down border-status-down/40",
+    degraded: "bg-status-degraded/15 text-status-degraded border-status-degraded/40",
+    neutral: "bg-surface-raised text-fg-muted border-border",
+  }[tone];
+
+  return (
+    <span className={`inline-flex items-center rounded-md border px-2 py-0.5 text-[11px] tracking-wide ${toneClass}`}>
+      {children}
+    </span>
+  );
+}