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.

server.ts

@@ -2,6 +2,7 @@ import { createServer } from "node:http";
 import next from "next";
 import { attachWebSocketServer } from "./lib/ws/server";
 import { configStore } from "./lib/config/loader";
+import { effectiveConfigStore } from "./lib/config/effective";
 import { collectorScheduler } from "./lib/collectors/scheduler";
 
 const port = Number(process.env.PORT ?? 3000);
@@ -17,8 +18,9 @@ async function main(): Promise<void> {
 
   configStore.load();
   configStore.watch();
-  collectorScheduler.start(configStore.get());
-  configStore.onUpdate((config) => collectorScheduler.reconcile(config));
+  await effectiveConfigStore.start();
+  collectorScheduler.start(effectiveConfigStore.get());
+  effectiveConfigStore.onUpdate((config) => collectorScheduler.reconcile(config));
 
   const httpServer = createServer((req, res) => {
     handle(req, res);
@@ -39,6 +41,7 @@ async function main(): Promise<void> {
 
   function shutdown(): void {
     collectorScheduler.stop();
+    effectiveConfigStore.stop();
     configStore.stop();
     httpServer.close(() => process.exit(0));
     setTimeout(() => process.exit(0), 5_000).unref();