Always keep a change output, so every tx stays fee-bumpable (B-62)

The max-amount checkbox sends amount_sats == the whole confirmed balance, so
change came out at 0, the change output was dropped, and the transaction had a
single output. bump_fee has nothing to shrink there: it raised RbfError every
30s until the reconciler abandoned the row six hours later. The RBF
single-change-output limitation was a documented gap, but the UI made it the
*default* withdrawal path.

The extra-input fallback would not have helped this case: a transaction moving
the entire balance already spends every UTXO the sender has. So the fix is at
build time — build_signed_transaction never produces a change output below
DUST_LIMIT_SATS, and never folds it into the fee either:

- withdrawals pass reduce_amount_to_keep_change=True and move a dust limit less.
  The fee already comes out of the withdrawn amount by design, so this is the
  same rule applied a little harder, and Withdrawal.amount_requested_sats vs
  amount_sent_sats already existed to record the difference.
- bets don't: the bet is a fixed price that can't be quietly reduced. A balance
  exactly equal to the bet is refused with balance_leaves_no_change (translated
  into all 7 languages, carrying required_extra_sats), which turns "a user's
  balance must never exactly equal the bet" from a documented assumption into an
  enforced one — and stops an unbumpable bet from holding a round open until the
  reconciler gives up on it.

bump_fee's no-change guard stays: a single-output tx broadcast before this
change can still be pending across the deploy, and it must fail loudly rather
than start shrinking a recipient's output. Its test now hand-builds that shape,
precisely because the builder no longer will.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

app/static/i18n.js

@@ -142,6 +142,7 @@ const TRANSLATIONS = {
     'error.round_full': 'This round has reached its maximum of {max_participants} players — wait for the next one, it opens shortly.',
     'error.already_betting': 'You already have an active bet in the current round.',
     'error.insufficient_balance': 'Insufficient balance.',
+    'error.balance_leaves_no_change': 'Your balance is too close to the bet amount: {required_extra_plm} PLM more are needed so the transaction keeps a change output and can be fee-bumped if the network is slow.',
     'error.balance_pending_confirmation': 'You have {pending_plm} PLM pending confirmation — it is not spendable yet.',
     'error.amount_below_network_fee': 'The amount is too small to cover the network fee.',
     'error.invalid_address': 'Not a valid PLM address (it must start with plm1q…).',
@@ -303,6 +304,7 @@ const TRANSLATIONS = {
     'error.round_full': 'Questo round ha raggiunto il massimo di {max_participants} giocatori — aspetta il prossimo, si apre tra poco.',
     'error.already_betting': 'Hai già una bet attiva nel round corrente.',
     'error.insufficient_balance': 'Saldo insufficiente.',
+    'error.balance_leaves_no_change': 'Il tuo saldo è troppo vicino all\'importo della giocata: servono {required_extra_plm} PLM in più perché la transazione mantenga un resto e possa essere rilanciata con fee più alta se la rete è lenta.',
     'error.balance_pending_confirmation': 'Hai {pending_plm} PLM in attesa di conferma — non ancora disponibili per la spesa.',
     'error.amount_below_network_fee': "L'importo è troppo basso per coprire la fee di rete.",
     'error.invalid_address': 'Indirizzo PLM non valido (deve iniziare con plm1q…).',
@@ -464,6 +466,7 @@ const TRANSLATIONS = {
     'error.round_full': 'Esta ronda ha alcanzado su máximo de {max_participants} jugadores: espera la siguiente, se abre en breve.',
     'error.already_betting': 'Ya tienes una apuesta activa en la ronda actual.',
     'error.insufficient_balance': 'Saldo insuficiente.',
+    'error.balance_leaves_no_change': 'Tu saldo está demasiado cerca del importe de la apuesta: hacen falta {required_extra_plm} PLM más para que la transacción conserve un cambio y pueda relanzarse con más comisión si la red va lenta.',
     'error.balance_pending_confirmation': 'Tienes {pending_plm} PLM pendientes de confirmación — todavía no se pueden gastar.',
     'error.amount_below_network_fee': 'El importe es demasiado pequeño para cubrir la comisión de red.',
     'error.invalid_address': 'Dirección PLM no válida (debe empezar por plm1q…).',
@@ -625,6 +628,7 @@ const TRANSLATIONS = {
     'error.round_full': 'Ce tour a atteint son maximum de {max_participants} joueurs — attendez le prochain, il ouvre dans un instant.',
     'error.already_betting': 'Vous avez déjà une mise active dans le round en cours.',
     'error.insufficient_balance': 'Solde insuffisant.',
+    'error.balance_leaves_no_change': 'Votre solde est trop proche du montant de la mise : il faut {required_extra_plm} PLM de plus pour que la transaction garde une monnaie de rendu et puisse être relancée avec des frais plus élevés si le réseau est lent.',
     'error.balance_pending_confirmation': 'Vous avez {pending_plm} PLM en attente de confirmation — pas encore disponibles.',
     'error.amount_below_network_fee': 'Le montant est trop faible pour couvrir les frais de réseau.',
     'error.invalid_address': 'Adresse PLM invalide (elle doit commencer par plm1q…).',
@@ -786,6 +790,7 @@ const TRANSLATIONS = {
     'error.round_full': 'Diese Runde hat ihr Maximum von {max_participants} Spielern erreicht — warten Sie auf die nächste, sie beginnt in Kürze.',
     'error.already_betting': 'Du hast bereits eine aktive Wette in der laufenden Runde.',
     'error.insufficient_balance': 'Nicht genügend Guthaben.',
+    'error.balance_leaves_no_change': 'Ihr Guthaben liegt zu nah am Einsatzbetrag: Es werden {required_extra_plm} PLM mehr benötigt, damit die Transaktion einen Wechselgeld-Ausgang behält und bei langsamem Netz mit höherer Gebühr neu gesendet werden kann.',
     'error.balance_pending_confirmation': 'Sie haben {pending_plm} PLM, die noch auf Bestätigung warten — noch nicht verfügbar.',
     'error.amount_below_network_fee': 'Der Betrag ist zu klein, um die Netzwerkgebühr zu decken.',
     'error.invalid_address': 'Keine gültige PLM-Adresse (sie muss mit plm1q… beginnen).',
@@ -947,6 +952,7 @@ const TRANSLATIONS = {
     'error.round_full': 'В этом раунде достигнут максимум участников ({max_participants}) — дождитесь следующего, он начнётся совсем скоро.',
     'error.already_betting': 'У вас уже есть активная ставка в текущем раунде.',
     'error.insufficient_balance': 'Недостаточно средств.',
+    'error.balance_leaves_no_change': 'Ваш баланс слишком близок к сумме ставки: нужно ещё {required_extra_plm} PLM, чтобы в транзакции остался выход сдачи и её можно было переотправить с более высокой комиссией, если сеть работает медленно.',
     'error.balance_pending_confirmation': 'У вас есть {pending_plm} PLM, ожидающих подтверждения — они пока недоступны для расходования.',
     'error.amount_below_network_fee': 'Сумма слишком мала, чтобы покрыть комиссию сети.',
     'error.invalid_address': 'Некорректный адрес PLM (он должен начинаться с plm1q…).',
@@ -1108,6 +1114,7 @@ const TRANSLATIONS = {
     'error.round_full': '本轮已达到 {max_participants} 名玩家的上限 —— 请等待下一轮，很快就会开始。',
     'error.already_betting': '你在当前回合已有一笔有效下注。',
     'error.insufficient_balance': '余额不足。',
+    'error.balance_leaves_no_change': '您的余额与投注金额过于接近：还需要 {required_extra_plm} PLM，交易才能保留找零输出，并在网络拥堵时提高手续费重新广播。',
     'error.balance_pending_confirmation': '您有 {pending_plm} PLM 待确认 —— 尚不可用于支出。',
     'error.amount_below_network_fee': '金额太小，不足以支付网络手续费。',
     'error.invalid_address': 'PLM 地址无效（必须以 plm1q… 开头）。',