feat: system/http/traefik collectors and docker auto-discovery (M3)

Adds the remaining monitor types: a systeminformation-backed system
widget (single-flight cached so multiple widgets don't force
concurrent samples), an http widget with per-widget consecutive-
failure tracking, and a traefik widget that reads router/entrypoint/
middleware status from Traefik's own API. Also adds opt-in label-based
docker auto-discovery (discovery.docker in config.yml): containers
carrying traefik.enable=true are turned into docker widgets in a
synthetic "Discovered" group, re-scanned on a timer and whenever
config.yml changes, with manual widgets always taking precedence over
a discovered one for the same container.

Fixes a real bug surfaced while testing discovery: Next's App Router
bundles app/** through its own compiler pass, separate from server.ts
(run directly via tsx), so configStore/effectiveConfigStore were
silently instantiated twice - one instance watched and updated by
server.ts, another frozen instance read by SSR. Live config edits were
never reflected on page load without a full process restart. Both
stores now key their singleton off globalThis, which both module
graphs share within the same process.

Verified against a real Traefik v3 container (API-driven router list,
ping-based http check) and a labeled nginx container (auto-discovery),
including that a config.yml edit now shows up in a fresh page load
without restarting the server, in both dev and the production build.

components/widgets/registry.ts

@@ -4,6 +4,9 @@ import { BookmarkWidget } from "./bookmark/Widget";
 import { SearchWidget } from "./search/Widget";
 import { DockerWidget } from "./docker/Widget";
 import { DatabaseWidget } from "./database/Widget";
+import { SystemWidget } from "./system/Widget";
+import { HttpWidget } from "./http/Widget";
+import { TraefikWidget } from "./traefik/Widget";
 
 type WidgetComponent<T extends Widget["type"]> = ComponentType<{
   widget: Extract<Widget, { type: T }>;
@@ -15,4 +18,7 @@ export const widgetRegistry: { [K in Widget["type"]]: WidgetComponent<K> } = {
   search: SearchWidget,
   docker: DockerWidget,
   database: DatabaseWidget,
+  system: SystemWidget,
+  http: HttpWidget,
+  traefik: TraefikWidget,
 };