Proposal: Adjusted navigation logic for irregular layouts (Dice Roll)

[securesigner]

This PR proposes an adjustment to the keyboard navigation behavior discussed in issue #555. Currently, on the "Dice Roll" screen, pressing "Down" from the "6" key wraps to the top of the screen because there is no key directly below it.

This change modifies get_key_below to scan leftward for the nearest available key when entering the last row (in this case, snapping to "DEL").

Note: I am aware this touches on the broader discussion in #555 regarding layout changes. This PR explores a logic-based solution to the navigation "dead zones" rather than a layout-based one, to see if it offers a smoother UX without requiring visual redesigns.

[newtonick]

tested and confirmed fix

[kdmukai]

I'm mostly a concept NACK.

This PR takes just one part of the discussion in #555 but disregards the rather in-depth nuance and blended solution discussed (modifying the key layout itself in many screens) which obviates the need for this change in most cases.

This remains a challenging screen even after that discussion.

A further minor annoyance: The behavior as it is currently implemented was intentional (and, again, thoroughly discussed in the Issue). It is grating to see this PR described as "fixes a navigation bug."