refactor(test): extract blank canvas click position to DefaultGraphPositions

Replace hardcoded { x: 50, y: 500 } click positions in copyPaste.spec.ts
with a named emptyCanvasClick constant in DefaultGraphPositions.

Fixes #10330

browser_tests/fixtures/constants/defaultGraphPositions.ts

@@ -10,6 +10,7 @@ export const DefaultGraphPositions = {
   textEncodeNode2: { x: 622, y: 400 },
   textEncodeNodeToggler: { x: 430, y: 171 },
   emptySpaceClick: { x: 35, y: 31 },
+  emptyCanvasClick: { x: 50, y: 500 },
 
   // Slot positions
   clipTextEncodeNode1InputSlot: { x: 427, y: 198 },
@@ -39,6 +40,7 @@ export const DefaultGraphPositions = {
   textEncodeNode2: Position
   textEncodeNodeToggler: Position
   emptySpaceClick: Position
+  emptyCanvasClick: Position
   clipTextEncodeNode1InputSlot: Position
   clipTextEncodeNode2InputSlot: Position
   clipTextEncodeNode2InputLinkPath: Position

browser_tests/tests/copyPaste.spec.ts

@@ -146,7 +146,9 @@ test.describe('Copy Paste', { tag: ['@screenshot', '@workflow'] }, () => {
       const ksamplerNodes =
         await comfyPage.nodeOps.getNodeRefsByType('KSampler')
       await ksamplerNodes[0].copy()
-      await comfyPage.canvas.click({ position: { x: 50, y: 500 } })
+      await comfyPage.canvas.click({
+        position: DefaultGraphPositions.emptyCanvasClick
+      })
       await comfyPage.nextFrame()
       await comfyPage.clipboard.paste()
       await expect
@@ -182,7 +184,9 @@ test.describe('Copy Paste', { tag: ['@screenshot', '@workflow'] }, () => {
       await expect.poll(() => comfyPage.nodeOps.getGraphNodesCount()).toBe(3)
 
       // Step 3: Click empty canvas area, paste image → creates new LoadImage
-      await comfyPage.canvas.click({ position: { x: 50, y: 500 } })
+      await comfyPage.canvas.click({
+        position: DefaultGraphPositions.emptyCanvasClick
+      })
       await comfyPage.nextFrame()
 
       const uploadPromise2 = comfyPage.page.waitForResponse(