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.

app/page.tsx

@@ -1,4 +1,5 @@
-import { configStore, ConfigError } from "@/lib/config/loader";
+import { ConfigError } from "@/lib/config/loader";
+import { effectiveConfigStore } from "@/lib/config/effective";
 import { Dashboard } from "@/components/layout/Dashboard";
 
 export const dynamic = "force-dynamic";
@@ -6,7 +7,7 @@ export const dynamic = "force-dynamic";
 export default function Home() {
   let config;
   try {
-    config = configStore.get();
+    config = effectiveConfigStore.get();
   } catch (err) {
     const message = err instanceof ConfigError ? err.message : "Unknown configuration error";
     return (