fix: size ecash redeem sheet to its content

[NateMoeller]

The Redeem sheet opened from a sent ecash note used a fixed 33% height, which clipped the "Redeem when online" button and fee lines.

• Add an opt-in fitContent flag to showAppModalBottomSheet: the sheet sizes to its content, capped at 90% of the screen, and scrolls beyond that. Existing callers are unchanged.
• Use it for both ecash redeem entry points (transaction details and scan/paste).
• Add bottom padding to EcashRedeemPrompt so the last element doesn't sit flush against the sheet edge.