Image Slider Arrow buttons should have a border radius control

[dancounsell]

Add support for adjusting the border radius of the arrow buttons in the Image Slider Component

[dancounsell]

@cursoragent Can you fix this?

[cursor]

Yes — I’m on it.

• I’m going to pull the current PR branch, reproduce what’s broken with the new arrow button border radius control, and trace the value from the control → generated styles → rendered arrow buttons.
• Then I’ll fix the wiring (and any pack JSON/export defaults if needed), run the relevant checks, and push an updated commit to the PR branch.