Two-step add-funds modal instead of wallet redirect on insufficient balance

When a user hits an action they can't afford (e.g. creating a QR code with
0/low balance), open an in-app two-step modal instead of bouncing them to the
central wallet page. Step 1 explains pay-as-you-go billing + shows the action
cost and current balance; step 2 takes an amount and starts a Paystack checkout
via the central identity wallet-topup API, returning the user where they were.

- service-topup-modal: rebuilt as two-step (billing explainer -> amount/pay)
- IdentityClient::walletTopup + WalletTopupController + POST /wallet/topup
- balanceGate.openTopup / qrCustomizer.redirectTopup now prefer the modal,
  falling back to the wallet page only when no modal is wired
- qr-codes index + create render the modal and open it on insufficient balance

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

routes/web.php

@@ -2,6 +2,7 @@
 
 use App\Http\Controllers\Auth\SsoLoginController;
 use App\Http\Controllers\WalletBalanceController;
+use App\Http\Controllers\WalletTopupController;
 use App\Http\Controllers\NotificationController;
 use App\Http\Controllers\Public\QrScanController;
 use App\Http\Controllers\Qr\AccountController;
@@ -36,6 +37,7 @@ Route::get('/q/{shortCode}/app-icon', [QrScanController::class, 'appIcon'])->nam
 
 Route::middleware(['auth', 'platform.session'])->group(function () {
     Route::get('/wallet/balance', [WalletBalanceController::class, 'balance'])->name('wallet.balance');
+    Route::post('/wallet/topup', [WalletTopupController::class, 'store'])->name('user.wallet.topup');
     Route::get('/notifications', [NotificationController::class, 'index'])->name('notifications.index');
     Route::get('/notifications/unread', [NotificationController::class, 'unread'])->name('notifications.unread');
     Route::post('/notifications/{id}/read', [NotificationController::class, 'markAsRead'])->name('notifications.mark-read');