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

docker-compose.yml

@@ -0,0 +1,38 @@
+services:
+  backend:
+    build:
+      context: .
+      dockerfile: Dockerfile.backend
+    restart: unless-stopped
+    environment:
+      SECRET_KEY: ${SECRET_KEY:-change_me_in_production}
+      SQLITE_PATH: /app/data/homelab.db
+      CONFIG_PATH: /app/config.yml
+      CORS_ORIGINS: '["http://localhost:3000"]'
+    volumes:
+      - backend_data:/app/data
+      - ./backend/config.yml:/app/config.yml
+    networks:
+      - homelable
+    # Required for ping-based status checks
+    cap_add:
+      - NET_RAW
+
+  frontend:
+    build:
+      context: .
+      dockerfile: Dockerfile.frontend
+    restart: unless-stopped
+    ports:
+      - "3000:80"
+    depends_on:
+      - backend
+    networks:
+      - homelable
+
+volumes:
+  backend_data:
+
+networks:
+  homelable:
+    driver: bridge