Fix ButtonWidget default size to match SAIL

[jenniferhiga]

Fix default size so STANDARD matches SAIL's default rendering (text-base currently aliases to text-sm).

Current Issue: SAIL default renders larger than Sailwind's STANDARD.

Current Workaround: Explicitly set size: MEDIUM on ButtonWidget to match SAIL's default rendering

Reference: Restaurant Order PR

[pglevy]

Open to making adjustments here but less concerned about what SAIL is than what we think the scale should be. The SAIL options seem to be missing a step, with small and standard being close and then a jump to large (34, 38, 49). (Also, standard buttons actually take up 40px of space in the layout because of some built-in margin. 🤷‍♂️)

The intent is not to be pixel-perfect with SAIL. And if we have something we like better, we can change SAIL.