fix: clear card funding errors and toast feedback on transfer

Why

On staging, a 2000 USD wallet → card top-up failed because reserve.CARD_USD held 913.81. The app showed a raw native Alert: "Insufficient balance on account ". Nothing was debited; the transaction rolled back.

Backend

Error message

• postDoubleEntry now throws InsufficientAccountBalanceException, which still extends BadRequestException.
• The client-facing message no longer contains the account id. The id is logged server side instead.

Card deposit and card withdraw

• A CARD_USD system-account shortfall now returns 422 CARD_FUNDING_UNAVAILABLE.
• That case also logs an ALERT: line with a hint that depends on the account type:
  • reserve.CARD_USD: top up the KeySecure reserve
  • normal.CARD_USD: mirror drift
• A shortfall on the user's wallet or card stays INSUFFICIENT_BALANCE.
• Withdraw: a user asking for more than their card balance gets INSUFFICIENT_BALANCE, with no false ALERT. This applies only to a real CARD_USD shortfall error; DB and lock errors are not remapped.

Frontend

• A new funding-unavailable kind maps the new code, with separate top-up and withdraw copy.
• transfer-form.tsx now shows every error as a toast through showErrorMessage instead of Alert.alert.
  • Raw backend text is never shown, except the wrong-passcode message.
  • The sheets are closed before the toast appears.

Verification

• be: card-account and transactions jest pass (300 card-account tests); yarn build is clean.
• fe: type-check is clean, lint has 0 errors, transfer and card-account tests pass.
• The Opus review gate passed in round 2. The NIT fixes come after it.
• Pre-existing and unrelated: admin-lending.risk.spec.ts fails at BASE with a DI error.

Follow-ups

• Two concurrent withdraws can very rarely trigger a false ALERT, because the account snapshot is read before the transaction.
• The wrong-passcode toast sits under the passcode sheet backdrop.

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