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/canvas/CanvasContainer.tsx

@@ -1,4 +1,4 @@
-import { useCallback, useState } from 'react'
+import { useCallback, useEffect, useState } from 'react'
 import {
   ReactFlow,
   Background,
@@ -7,6 +7,7 @@ import {
   BackgroundVariant,
   ConnectionMode,
   SelectionMode,
+  useReactFlow,
   type Node,
   type Edge,
   type Connection,
@@ -33,7 +34,19 @@ export function CanvasContainer({ onConnect: onConnectProp, onEdgeDoubleClick, o
     nodes, edges,
     onNodesChange, onEdgesChange,
     setSelectedNode, snapshotHistory,
+    fitViewPending, clearFitViewPending,
   } = useCanvasStore()
+  const { fitView } = useReactFlow()
+
+  // Fit view after canvas loads (fitViewPending is set by 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 activeTheme = useThemeStore((s) => s.activeTheme)
   const theme = THEMES[activeTheme]
@@ -77,7 +90,6 @@ export function CanvasContainer({ onConnect: onConnectProp, onEdgeDoubleClick, o
         multiSelectionKeyCode={['Meta', 'Control']}
         snapToGrid
         snapGrid={[16, 16]}
-        fitView
         colorMode={theme.colors.reactFlowColorMode}
         elevateNodesOnSelect={false}
         connectionMode={ConnectionMode.Loose}