fix: purchase split rebalancing and input focus issues

- Add onBlur handler to Input component for rebalancing on blur
- Rewrite rebalancePurchaseSplit to calculate delta vs total and distribute
- Extract ParticipantSplitInputs component with proper SolidJS reactivity
- Button shows 'Balance' when validation fails, 'Save' when valid
- Add i18n keys for purchaseBalanceAction and purchaseRebalanceAction

apps/miniapp/src/i18n.ts

@@ -159,6 +159,8 @@ export const dictionary = {
     paymentEditorBody: 'Review the payment record in one focused editor.',
     deletingPayment: 'Deleting payment…',
     purchaseSaveAction: 'Save purchase',
+    purchaseBalanceAction: 'Balance',
+    purchaseRebalanceAction: 'Rebalance',
     purchaseDeleteAction: 'Delete',
     deletingPurchase: 'Deleting purchase…',
     savingPurchase: 'Saving purchase…',
@@ -460,6 +462,8 @@ export const dictionary = {
     paymentEditorBody: 'Проверь оплату в отдельном редакторе.',
     deletingPayment: 'Удаляем оплату…',
     purchaseSaveAction: 'Сохранить покупку',
+    purchaseBalanceAction: 'Сбалансировать',
+    purchaseRebalanceAction: 'Перераспределить',
     purchaseDeleteAction: 'Удалить',
     deletingPurchase: 'Удаляем покупку…',
     savingPurchase: 'Сохраняем покупку…',