feat: Phase 3 & 4 — monitoring, discovery, polish, deployment

Phase 3 — Discovery & Monitoring:
- Network scanner: nmap wrapper + mock fallback, fingerprint service (35 signatures)
- Status checker: ping/http/https/tcp/ssh/prometheus/health per-node checks
- APScheduler: status checks every 60s, WebSocket broadcast
- WebSocket /ws/status: live node status updates to frontend
- Sidebar panels: Pending Devices, Hidden Devices, Scan History
- Auth token persisted to localStorage (survive page refresh)
- 24 new backend tests (scan flow + status_checker)

Phase 4 — Polish & Deployment:
- Auto-layout: Dagre hierarchical TB via Toolbar button
- Export PNG: html-to-image download via Toolbar button
- Scan config modal: CIDR ranges + check interval, GET/POST /api/v1/scan/config
- Dockerfile.backend (Python 3.13 slim + nmap), Dockerfile.frontend (nginx)
- docker-compose.yml with data volume and NET_RAW cap for ping
- scripts/lxc-install.sh: Proxmox VE systemd bootstrap
- README.md: quick-start, config reference, stack overview

frontend/src/api/client.ts

@@ -40,3 +40,15 @@ export const edgesApi = {
   create: (data: object) => api.post('/edges', data),
   delete: (id: string) => api.delete(`/edges/${id}`),
 }
+
+export const scanApi = {
+  trigger: () => api.post('/scan/trigger'),
+  pending: () => api.get('/scan/pending'),
+  hidden: () => api.get('/scan/hidden'),
+  runs: () => api.get('/scan/runs'),
+  approve: (id: string, nodeData: object) => api.post(`/scan/pending/${id}/approve`, nodeData),
+  hide: (id: string) => api.post(`/scan/pending/${id}/hide`),
+  ignore: (id: string) => api.post(`/scan/pending/${id}/ignore`),
+  getConfig: () => api.get<{ ranges: string[]; interval_seconds: number }>('/scan/config'),
+  saveConfig: (data: { ranges: string[]; interval_seconds: number }) => api.post('/scan/config', data),
+}