feat: add hardware specs to nodes (CPU, RAM, Disk) with canvas display

- Add cpu_count, cpu_model, ram_gb, disk_gb, show_hardware fields to NodeData
- NodeModal: collapsible Hardware section with toggle to show specs on canvas
- BaseNode: 2-line hardware section with Cpu/MemoryStick/HardDrive icons, only renders set fields
- DetailPanel: Hardware section with GB/TB formatting
- Backend: schema, model, DB migration, canvas save/load support
- Tests: frontend (NodeModal, DetailPanel) + backend (canvas persist/load)

frontend/src/types/index.ts

@@ -56,6 +56,11 @@ export interface NodeData extends Record<string, unknown> {
   last_seen?: string
   response_time_ms?: number
   notes?: string
+  cpu_count?: number
+  cpu_model?: string
+  ram_gb?: number
+  disk_gb?: number
+  show_hardware?: boolean
   parent_id?: string
   container_mode?: boolean
   custom_colors?: {