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/package.json

@@ -28,8 +28,10 @@
     "lucide-react": "^0.545.0",
     "react": "^18.3.1",
     "react-dom": "^18.3.1",
+    "recharts": "^3.10.1",
     "tailwind-merge": "^3.3.1",
-    "tw-animate-css": "^1.4.0"
+    "tw-animate-css": "^1.4.0",
+    "wouter": "^3.11.0"
   },
   "devDependencies": {
     "@tailwindcss/vite": "^4.1.13",