Bring canvas buttons to same z-index level

[VaidikFlow]

Bring canvas buttons to z-index 10 so that they do not show over top containers using embedded canvas

[gemini-code-assist]

Code Review

This pull request adjusts z-index values for UI components in the agentflow package to manage layering. Feedback highlights a formatting issue and a logic inconsistency in the ValidationFeedback component where the button and its associated overlay have mismatched z-indices. Furthermore, the reduction of Z_INDEX_DRAWER in the node palette impacts both the trigger and the overlay, potentially causing the drawer to be obscured by other canvas elements; it is recommended to use separate z-index values for these components.

[jocelynlin-wd]

looks like the add node button is fixed, but not the validation button.
when a modal is opened, add nodes is rendered correctly but validate button still not correct

[jocelynlin-wd]

I believe this change is actually not necessary, since we want the button to be more visible when validate is clicked? @j-sanaa what do you think?

[j-sanaa]

I agree with this. To me it makes sense to have the validation panel visible on top of other UI elements when clicked