Add wallet balance widget to the profile menu (after Billing)

Wallet balance peek rendered as a menu row directly under Billing, backed by
a /wallet/balance endpoint (BillingClient) and guarded by Route::has. Also
opens Afia via a direct window event for reliability.

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

config/billing.php

@@ -4,4 +4,6 @@ return [
     'api_url' => env('BILLING_API_URL', 'https://ladill.com/api/billing'),
     'api_key' => env('BILLING_API_KEY_EVENTS'),
     'service' => 'events',
+    'wallet_balance_route' => 'wallet.balance',
+    'currency' => 'GHS',
 ];