feat: amount screens share the centred, edge-to-edge layout #1083

What should change?

The amount screens could adopt the USDT Figma layout together: the amount centred in the free space above the controls, and a keypad that spans the sheet edge to edge. Today all three send amount flows (on-chain, Lightning and USDT) keep the amount at the top and the keypad inside 16 pt side insets.

Why separate

#1056 asked for the centred amount and the edge-to-edge keypad on the USDT Amount step only. In review, @pwltr asked to keep USDT consistent with the Bitcoin screens and to make any redesign one change across all three flows (iOS, Android). #1061 and synonymdev/bitkit-android#1636 therefore fixed only the keypad gap above Continue.

Design

Bitkit - Refactor v63 › Send (USDT) › Amount USDT. There is no matching frame yet for the Bitcoin amount screens; a design decision is needed before implementation.

Notes

• Android has the same layout and would change together.
• The edge keys need hit testing at the sheet edges, as checked on the earlier USDT-only version.