Fix(agentflow) - Fix z-index for validation button

[j-sanaa]

Before:

After:

• Revert changes made to z-index of validation panel

[gemini-code-assist]

Code Review

This pull request updates the zIndex values for the sparkles icon button and the canvas action buttons wrapper in Agentflow.tsx, reducing them from 1001 to 10. The review feedback points out that this change introduces a stacking conflict with the AddNodesDrawer, which may cause UI elements to overlap incorrectly. Additionally, the feedback notes that the zIndex on the action buttons wrapper is redundant and recommends using centralized constants instead of magic numbers to maintain a consistent stacking hierarchy.

[mmattu-wd]

Thanks for making this change! I think we should potentially explore a stack manager so we never have to define a zIndex manually again

[jocelynlin-wd]

thanks for looking into this!