fix: resolve flaky color picker test by adding missing await (#5467)

- Add missing await for async getProperty call in selectionToolbox test
- Add timestamp to test username generation to prevent duplicate user conflicts
- Test now passes consistently without race conditions

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-authored-by: Claude <noreply@anthropic.com>

browser_tests/tests/selectionToolbox.spec.ts

@@ -149,7 +149,7 @@ test.describe('Selection Toolbox', () => {
       // Node should have the selected color class/style
       // Note: Exact verification method depends on how color is applied to nodes
       const selectedNode = (await comfyPage.getNodeRefsByTitle('KSampler'))[0]
-      expect(selectedNode.getProperty('color')).not.toBeNull()
+      expect(await selectedNode.getProperty('color')).not.toBeNull()
     })
 
     test('color picker shows current color of selected nodes', async ({