feat: replace static hardware fields with dynamic node properties

Replaces the 4 fixed hardware columns (cpu_count, cpu_model, ram_gb,
disk_gb) with a flexible properties system. Each property has a key,
value, icon (from a curated Lucide picker), and a visibility toggle
that controls whether it appears on the canvas node card.

- Backend: add `properties` JSON column to Node model; data migration
  converts existing hardware rows to properties with correct icons
  (idempotent, old columns kept for safety)
- Backend: add `properties` to NodeBase, NodeUpdate, NodeSave schemas
  and canvasSerializer so values survive canvas save/load
- Frontend: add NodeProperty type; new propertyIcons.ts registry (20
  icons); BaseNode renders visible properties with legacy hardware
  fallback for unmigrated nodes
- Frontend: DetailPanel gains interactive properties section (add /
  edit / remove / toggle visibility / icon picker) replacing the
  read-only hardware block; hardware section removed from NodeModal
- Tests: 6 migration tests, 7 API tests, 8 DetailPanel property tests,
  6 BaseNode render/fallback tests, 9 propertyIcons util tests

frontend/src/utils/propertyIcons.ts

@@ -0,0 +1,53 @@
+import {
+  Battery,
+  Box,
+  Clock,
+  Cpu,
+  Database,
+  Globe,
+  HardDrive,
+  Hash,
+  Key,
+  Layers,
+  Link,
+  MemoryStick,
+  Monitor,
+  Network,
+  Server,
+  Shield,
+  Tag,
+  Thermometer,
+  Wifi,
+  Zap,
+} from 'lucide-react'
+import type { LucideIcon } from 'lucide-react'
+
+export const PROPERTY_ICONS: Record<string, LucideIcon> = {
+  Battery,
+  Box,
+  Clock,
+  Cpu,
+  Database,
+  Globe,
+  HardDrive,
+  Hash,
+  Key,
+  Layers,
+  Link,
+  MemoryStick,
+  Monitor,
+  Network,
+  Server,
+  Shield,
+  Tag,
+  Thermometer,
+  Wifi,
+  Zap,
+}
+
+export const PROPERTY_ICON_NAMES = Object.keys(PROPERTY_ICONS) as (keyof typeof PROPERTY_ICONS)[]
+
+export function resolvePropertyIcon(name: string | null | undefined): LucideIcon | null {
+  if (!name) return null
+  return PROPERTY_ICONS[name] ?? null
+}