feat: configurable bottom handles, scanner rewrite, UI polish

## New features
- Configurable bottom connection points per node (1–4 handles)
- Fit view on load
- LiveView improvements
- Node modal: inline Type/Icon picker, default icon in trigger
- Remove redundant Save button from ScanConfigModal

## Scanner fixes
- Phase 1: replace nmap ARP sweep with concurrent asyncio ping sweep
  (50 parallel pings, 1s timeout). Zero false positives, works in any
  Docker network mode. Supplements with /proc/net/arp for ICMP-blocked devices.
- Phase 2: explicit -sS (root) / -sT (non-root) scan type; bump
  host-timeout to 60s; gather(return_exceptions=True) so one failing
  host doesn't abort the batch
- Fix 404 on missing device in hide/ignore
- Validate CIDR ranges to prevent nmap injection
- Thread-safe cancel set, pre-fetch canvas/hidden IPs (no N+1 queries)
- Logging: attach StreamHandler to root logger so app.* logs are visible

## Tests
- 21 backend scanner tests (ping sweep, ARP cache, Phase 2 tolerance)
- Full NodeModal coverage (53 tests)
- LiveView, store, edge label tests

frontend/src/components/LiveView.tsx

@@ -18,6 +18,7 @@ import {
   BackgroundVariant,
   Controls,
   ConnectionMode,
+  useReactFlow,
   type Node,
 } from '@xyflow/react'
 import '@xyflow/react/dist/style.css'
@@ -36,7 +37,8 @@ const STORAGE_KEY = 'homelable_canvas'
 type ViewState = 'loading' | 'disabled' | 'invalid-key' | 'no-key' | 'network-error' | 'ready'
 
 function LiveViewCanvas() {
-  const { nodes, edges, loadCanvas } = useCanvasStore()
+  const { nodes, edges, loadCanvas, fitViewPending, clearFitViewPending } = useCanvasStore()
+  const { fitView } = useReactFlow()
   const activeTheme = useThemeStore((s) => s.activeTheme)
   const theme = THEMES[activeTheme]
   // Derive initial view state synchronously (avoids calling setState inside an effect):
@@ -87,6 +89,15 @@ function LiveViewCanvas() {
       })
   }, [loadCanvas])
 
+  useEffect(() => {
+    if (!fitViewPending || nodes.length === 0) return
+    const id = setTimeout(() => {
+      fitView({ padding: 0.12, duration: 350 })
+      clearFitViewPending()
+    }, 50)
+    return () => clearTimeout(id)
+  }, [fitViewPending, nodes.length, fitView, clearFitViewPending])
+
   const onNodeClick = useCallback((_: React.MouseEvent, node: Node<NodeData>) => {
     const ip = node.data.ip
     if (ip) window.open(`http://${ip}`, '_blank', 'noopener,noreferrer')
@@ -129,7 +140,6 @@ function LiveViewCanvas() {
         elementsSelectable={false}
         panOnDrag
         zoomOnScroll
-        fitView
         colorMode={theme.colors.reactFlowColorMode}
         connectionMode={ConnectionMode.Loose}
         onNodeClick={onNodeClick}