Fix pos mode

[dewabisma]

Summary

• Handle payment intent that aware of different decimal separator
• Prevent stacking on top same screen when processing intent

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Note

Medium Risk
Changes how payment URL amounts are carried and parsed (wire amount vs localized/display text) and updates POS QR watch/matching logic to rely on raw BigInt values, which could impact payment flows if parsing/formatting expectations differ across locales.

Overview
POS mode now passes and validates raw planck amounts end-to-end. PosQrScreen takes amountPlanck: BigInt (instead of a formatted string), uses it directly for QR request generation and transfer matching, and shows an explicit error for invalid/zero amounts.

Payment-intent amount localization via AmountInputLogic was removed. parsePaymentUrlAmount/PaymentUrlAmountResult (and related unit tests) were deleted, PaymentIntent no longer exposes an amountPlanck helper, and the send flow now parses initialAmount differently for pay mode (parseWireAmount) vs normal send (parseQuanAmount). In pay mode, fiat flipping and the secondary "≈" display are disabled, and QR-scanned payment intents now populate the amount field with the raw URL amount string.

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