Refactor wallet balance handling and integrate PaymentService for centralized management

- Replaced direct wallet balance computation in Navbar and WalletPage with a centralized totalBalance property from PaymentService, improving code maintainability.
- Updated CreateProductDialog, CreateStoreDialog, and MerchantStore components to utilize PaymentService for retrieving wallet admin and invoice keys, enhancing consistency across the application.
- These changes streamline wallet management and improve the overall architecture of the wallet module.

src/components/layout/Navbar.vue

@@ -33,13 +33,12 @@ const { navigation: modularNavigation, userMenuItems } = useModularNavigation()
 
 const navigation = modularNavigation
 
-// Compute total wallet balance
-const totalBalance = computed(() => {
-  if (!auth.currentUser.value?.wallets) return 0
+// Get PaymentService from DI for centralized wallet balance
+const paymentService = tryInjectService(SERVICE_TOKENS.PAYMENT_SERVICE) as any
 
-  return auth.currentUser.value.wallets.reduce((total, wallet) => {
-    return total + (wallet.balance_msat || 0)
-  }, 0)
+// Use PaymentService for total wallet balance
+const totalBalance = computed(() => {
+  return paymentService?.totalBalance || 0
 })
 
 // Try to get chat service from DI (may not be available if chat module not loaded)