[support-3d] C9b. Tighten make_kiss for ball-circular-cushion

[ekiefl]

Sub-issue of #341.

Apply the same 3D treatment to ball-circular-cushion make_kiss that lands
in #345 for the linear case.

• Guard against z-drift
• Balls can't be pushed into the table

Blocked on #304. Progress here waits until #304 has a working
ball-circular-cushion geometry; the make_kiss formulation should mirror
whatever the detection routine assumes about the cushion surface.

Current implementation projects onto the xy-plane only. Since the circular
cushion is modeled as a vertical-axis cylinder, the xy projection is correct
for the cushion-distance solve, but the result needs table-floor enforcement
to prevent the success and fallback paths from placing balls below z = R.