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.

lib/types/widget-result.ts

@@ -1,3 +1,7 @@
+import type { SystemResult } from "./system-result";
+import type { HttpCheckResult } from "./http-result";
+import type { TraefikResult } from "./traefik-result";
+
 export interface DockerContainerResult {
   status: "running" | "exited" | "restarting" | "paused" | "dead" | "created" | "unknown";
   health: "healthy" | "unhealthy" | "starting" | "none";
@@ -13,4 +17,7 @@ export interface DockerContainerResult {
 export type WidgetResult =
   | { type: "docker"; data: DockerContainerResult }
   | { type: "database"; data: DockerContainerResult }
+  | { type: "system"; data: SystemResult }
+  | { type: "http"; data: HttpCheckResult }
+  | { type: "traefik"; data: TraefikResult }
   | { type: "error"; message: string };