Warn before a send or swap strands tokens

[j0ntz]

Description

A wallet that holds tokens needs its gas asset to move them. Nothing stops a user from
max-sending or max-swapping the whole gas balance, which strands every token left behind.

This adds a warning modal that fires before the transaction is signed, in both the send
and the swap flow:

• src/util/stuckFundsWarning.ts decides whether the pending transaction leaves the
  source wallet without enough gas to move what stays. The threshold is the
  transaction's own fee: a wallet that cannot afford one more transaction of the same
  size counts as drained.
• src/components/modals/StuckFundsWarningModal.tsx shows a plain ButtonsModal
  (warning border, Continue Anyway / Cancel) and resolves to a boolean.
• SendScene2.handleSliderComplete gates every send path (ramps, gift cards, FIO, scan,
  wallet list, transfer modal all funnel through send2).
• SwapConfirmationScene.handleSlideComplete gates swaps, where the real from-amount and
  network fee are known.

Two cases fire the warning, per the task's acceptance criteria:

1. The wallet holds a nonzero token balance and the transaction spends effectively all
   of the gas asset.
2. The wallet holds no tokens and the swap puts one in that same wallet while draining
   the gas needed to move it out.

UTXO chains cannot hit either case, so their behavior is unchanged.

Two cases are deliberately excluded, both raised in review:

• A same-wallet swap whose payout is the gas asset (the "buy gas" path) credits
  toNativeAmount back into the leftover-gas figure, so it does not warn.
• A transaction that spends a token discounts that amount from the token balance, so
  emptying the last token does not warn about tokens that will not be there.

The swap scene's terms-modal expiry deferral was generalized to cover any blocking modal,
so a quote cannot expire and close behind the warning while it is up.

Asana: https://app.asana.com/0/1215088146871429/1209102990528561

CHANGELOG

Does this branch warrant an entry to the CHANGELOG?

• Yes
• No

Dependencies

none

Requirements

If you have made any visual changes to the GUI. Make sure you have:

• Tested on iOS device
• Tested on Android device
• Tested on small-screen device (iPod Touch)
• Tested on large-screen device (tablet)

[j0ntz]

📸 Test evidence

max send fantom with tokens

stuck funds warning modal

cancel returns to send

send broadcast success

send txid onchain

max swap quote

swap stuck funds warning

swap cancel no execution

Captured by the agent's in-app test run (build-and-test).

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[j0ntz]

📸 Test evidence (after fix)

swap warning after fixes

swap warning final head

Captured by the agent's in-app test run (build-and-test).