feat: Allows users to toggle the "no perk" checkbox by clicking its label

Issue #124 (closed) pointed out that the "no perks, please" checkbox, despite being tiny, and despite having a huge label right next to it, couldn't be toggled by clicking or tapping its label - which is a common and reasonable-to-expect feature of HTML forms. Since the target checkbox is itself quite tiny, this was filed as a UX bug, and I agree.

This MR addresses this issue, and ensures that the mouse cursor will change to a pointer on rollover to indicate to a user that they can indeed tap it to toggle the checkbox.

Fixes #124 (closed).