Dynamic fee coverage display

Show donors the exact fee amount before they decide whether to cover it — "Add $1.53 so 100% of your $50 gift goes to us" — instead of vague language like "cover processing fees." Clarity drives opt-in rates higher than ambiguity ever does. The exact amount calculates in real time as the donor types or selects an amount. No deceptive defaults, no anchoring tricks, no Zeffy-style tip prompts — just an honest, opt-in choice.