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.

components/widgets/registry.ts

@@ -0,0 +1,13 @@
+import type { ComponentType } from "react";
+import type { Widget } from "@/lib/config/schema";
+import { BookmarkWidget } from "./bookmark/Widget";
+import { SearchWidget } from "./search/Widget";
+
+type WidgetComponent<T extends Widget["type"]> = ComponentType<{
+  widget: Extract<Widget, { type: T }>;
+}>;
+
+export const widgetRegistry: { [K in Widget["type"]]: WidgetComponent<K> } = {
+  bookmark: BookmarkWidget,
+  search: SearchWidget,
+};