Adds super user balance overview

Implements functionality for super users to view a breakdown of outstanding balances for all users.

This includes:
- Adding an API endpoint to fetch all user balances.
- Updating the frontend to display these balances in a table, accessible only to super users.
- Modifying the balance calculation for the current user to reflect the total owed by or to the castle for super users.

This provides super users with a comprehensive view of the castle's financial position.

crud.py

@@ -317,6 +317,43 @@ async def get_user_balance(user_id: str) -> UserBalance:
     )
 
 
+async def get_all_user_balances() -> list[UserBalance]:
+    """Get balances for all users (used by castle to see who they owe)"""
+    # Get all user-specific accounts
+    all_accounts = await db.fetchall(
+        "SELECT * FROM accounts WHERE user_id IS NOT NULL",
+        {},
+        Account,
+    )
+
+    # Group by user_id
+    users_dict = {}
+    for account in all_accounts:
+        if account.user_id not in users_dict:
+            users_dict[account.user_id] = []
+        users_dict[account.user_id].append(account)
+
+    # Calculate balance for each user
+    user_balances = []
+    for user_id, accounts in users_dict.items():
+        total_balance = 0
+        for account in accounts:
+            balance = await get_account_balance(account.id)
+            if account.account_type == AccountType.LIABILITY:
+                total_balance += balance
+            elif account.account_type == AccountType.ASSET:
+                total_balance -= balance
+
+        if total_balance != 0:  # Only include users with non-zero balance
+            user_balances.append(
+                UserBalance(
+                    user_id=user_id, balance=total_balance, accounts=accounts
+                )
+            )
+
+    return user_balances
+
+
 async def get_account_transactions(
     account_id: str, limit: int = 100
 ) -> list[tuple[JournalEntry, EntryLine]]: