feat: lasso selection, multi-select panel, and named groups

- Add lasso/box selection via selectionOnDrag (Space to pan, lasso by default)
- Add lasso/pan toggle button in canvas controls (bottom-left)
- Multi-select panel in right panel when 2+ nodes selected (including zones)
- Create named Group node from selected nodes with bounding box math
- Group node: resizable, inline rename, show/hide border toggle, status summary
- GroupDetailPanel: lists members, online/offline count, ungroup action
- Fix group persistence after save/reload (extend proxmox container map to include group nodes)
- Fix groupRect serialization to preserve parent_id
- Remove background color from group and proxmox container node wrappers
- Add tests for all new store actions, GroupNode, MultiSelectPanel, GroupDetailPanel

frontend/src/components/canvas/__tests__/CanvasContainer.test.tsx

@@ -16,8 +16,10 @@ vi.mock('@xyflow/react', () => ({
   },
   Background: () => null,
   Controls: () => null,
+  ControlButton: () => null,
   BackgroundVariant: { Dots: 'dots' },
   ConnectionMode: { Loose: 'loose' },
+  SelectionMode: { Partial: 'partial' },
 }))
 
 vi.mock('@xyflow/react/dist/style.css', () => ({}))
@@ -151,6 +153,55 @@ describe('CanvasContainer', () => {
     expect(rfProps.deleteKeyCode).toEqual(['Backspace', 'Delete'])
   })
 
+  // ── Lasso / multi-select ──────────────────────────────────────────────────
+
+  it('enables selectionOnDrag for lasso selection', () => {
+    render(<CanvasContainer />)
+    expect(rfProps.selectionOnDrag).toBe(true)
+  })
+
+  it('sets panActivationKeyCode to Space', () => {
+    render(<CanvasContainer />)
+    expect(rfProps.panActivationKeyCode).toBe('Space')
+  })
+
+  it('sets panOnDrag to [1, 2]', () => {
+    render(<CanvasContainer />)
+    expect(rfProps.panOnDrag).toEqual([1, 2])
+  })
+
+  it('sets selectionMode to Partial', () => {
+    render(<CanvasContainer />)
+    expect(rfProps.selectionMode).toBe('partial')
+  })
+
+  it('sets multiSelectionKeyCode to Meta and Control', () => {
+    render(<CanvasContainer />)
+    expect(rfProps.multiSelectionKeyCode).toEqual(['Meta', 'Control'])
+  })
+
+  it('clears selectedNode (sets null) on Ctrl+click instead of selecting', () => {
+    const node = makeNode('n1')
+    useCanvasStore.setState({ nodes: [node], selectedNodeId: 'n1' })
+    render(<CanvasContainer />)
+    ;(rfProps.onNodeClick as (...args: unknown[]) => unknown)(
+      { ctrlKey: true, metaKey: false } as unknown as MouseEvent,
+      node,
+    )
+    expect(useCanvasStore.getState().selectedNodeId).toBeNull()
+  })
+
+  it('clears selectedNode (sets null) on Cmd+click', () => {
+    const node = makeNode('n1')
+    useCanvasStore.setState({ nodes: [node], selectedNodeId: 'n1' })
+    render(<CanvasContainer />)
+    ;(rfProps.onNodeClick as (...args: unknown[]) => unknown)(
+      { ctrlKey: false, metaKey: true } as unknown as MouseEvent,
+      node,
+    )
+    expect(useCanvasStore.getState().selectedNodeId).toBeNull()
+  })
+
   // ── onBeforeDelete snapshot ───────────────────────────────────────────────
 
   it('onBeforeDelete calls snapshotHistory and returns true', async () => {