Adds fiat currency balances to user balances

Extends user balance information to include fiat currency balances,
calculated based on entry line metadata and account types.

This allows for a more comprehensive view of user balances,
including both satoshi and fiat currency holdings.

Updates the castle index template and API to display fiat balances.

views_api.py

@@ -420,9 +420,23 @@ async def api_get_my_balance(
     if wallet.wallet.user == lnbits_settings.super_user:
         all_balances = await get_all_user_balances()
         total_owed = sum(b.balance for b in all_balances if b.balance > 0)
+
+        # Aggregate fiat balances from all users
+        total_fiat_balances = {}
+        for user_balance in all_balances:
+            for currency, amount in user_balance.fiat_balances.items():
+                if currency not in total_fiat_balances:
+                    total_fiat_balances[currency] = 0.0
+                # Only add positive balances (what castle owes)
+                if amount > 0:
+                    total_fiat_balances[currency] += amount
+
         # Return as castle's "balance" - positive means castle owes money
         return UserBalance(
-            user_id=wallet.wallet.user, balance=total_owed, accounts=[]
+            user_id=wallet.wallet.user,
+            balance=total_owed,
+            accounts=[],
+            fiat_balances=total_fiat_balances,
         )
 
     # For regular users, show their individual balance