fix(sub v3): PAYG-related tweaks

[isabellaenriquez]

Closes BIL-1626, BIL-1647, BIL-1664, BIL-1676:

• Hitting Enter key with the PAYG in-line edit form active will submit the new budget
• Fixed bug where PAYG step overflowed for legacy tiers on smaller screens
• Renamed per-category spend limits to per-product in cart
• Made height consistent across rows in per-category PAYG info table

[linear]

BIL-1626 Rename per-category spend limits in cart

BIL-1647 [LEGACY TIERS] Make height consistent across rows in per-category PAYG table

BIL-1664 [LEGACY TIERS] PAYG step overflows on smaller screens

BIL-1676 PAYG in-line edit should save on enter key down