fix: memoize borderWidth and sync boxShadow glow ring with zoom

- Wrap borderWidth in useMemo to avoid re-computing on unrelated renders
- Replace hardcoded 1px in boxShadow with borderWidth so glow ring
  matches border thickness at all zoom levels
- Add useViewport mock + 4 zoom-scaling tests to BaseNode.test.tsx

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

@@ -5,11 +5,14 @@ import { BaseNode } from '../nodes/BaseNode'
 import type { NodeData } from '@/types'
 import type { Node } from '@xyflow/react'
 
+let mockZoom = 1
+
 vi.mock('@xyflow/react', () => ({
   Handle: () => null,
   Position: { Top: 'top', Bottom: 'bottom' },
   NodeResizer: () => null,
   useUpdateNodeInternals: () => vi.fn(),
+  useViewport: () => ({ zoom: mockZoom }),
 }))
 
 vi.mock('@/stores/themeStore', () => ({
@@ -85,6 +88,37 @@ function renderBaseNode(data: Partial<NodeData>) {
   )
 }
 
+describe('BaseNode — borderWidth zoom scaling', () => {
+  it('borderWidth is 1px at zoom=1', () => {
+    mockZoom = 1
+    const { container } = renderBaseNode({})
+    expect((container.firstChild as HTMLElement).style.borderWidth).toBe('1px')
+  })
+
+  it('borderWidth scales to 2px at zoom=0.5', () => {
+    mockZoom = 0.5
+    const { container } = renderBaseNode({})
+    expect((container.firstChild as HTMLElement).style.borderWidth).toBe('2px')
+  })
+
+  it('borderWidth is clamped to 1px at zoom=2', () => {
+    mockZoom = 2
+    const { container } = renderBaseNode({})
+    expect((container.firstChild as HTMLElement).style.borderWidth).toBe('1px')
+  })
+
+  it('boxShadow glow ring uses borderWidth when selected + online at zoom=0.5', () => {
+    mockZoom = 0.5
+    const node = makeNode({ status: 'online' })
+    const { container } = render(
+      <BaseNode id={node.id} data={node.data} selected={true} icon={Server}
+        type="server" dragging={false} zIndex={0} isConnectable={true}
+        positionAbsoluteX={0} positionAbsoluteY={0} />
+    )
+    expect((container.firstChild as HTMLElement).style.boxShadow).toContain('0 0 0 2px')
+  })
+})
+
 describe('BaseNode — properties rendering', () => {
   it('renders visible properties on the node', () => {
     renderBaseNode({