feat: external importers + uptime monitors (merge plan M1)

Two tracks from the Beszel/Domain-Locker merge plan in ROADMAP.md:

- Importers: POST /api/import/external sniffs Homepage services.yml,
  Homarr JSON, and Dashy conf.yml into sections/items; SettingsDialog
  import now accepts all four formats.
- Monitors (M1): monitors + heartbeats schema, pure checkers for
  http/tcp/ping/dns/keyword/json-query/push, scheduler on app ctx,
  CRUD + check-now + push ingest API, /monitors + /monitors/:id pages
  (wouter), monitor board widget, ServiceDialog monitor opt-in.

Authored By: TDvorak <[email protected]>

Generated with Devin (https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

apps/frontend/src/widgets/index.tsx

@@ -3,6 +3,7 @@ import type { Item } from "@/types";
 import { ClockWidget } from "@/widgets/clock";
 import { PiholeWidget, AdguardWidget } from "@/widgets/blocker";
 import { ImmichWidget } from "@/widgets/immich";
+import { MonitorWidget } from "@/widgets/monitor";
 
 // WidgetHost seam: renderers own the tile chrome; this maps config.type to
 // the component that fills it. Adding a widget = one fetcher in Go + one
@@ -28,6 +29,7 @@ const registry: WidgetRegistry = {
 	pihole: { view: PiholeWidget },
 	adguard: { view: AdguardWidget },
 	immich: { view: ImmichWidget },
+	monitor: { view: MonitorWidget },
 };
 
 export function cfgStr(item: Item, key: string): string {