Adds settle receivable functionality

Implements a "Settle Receivable" feature for super users to record manual payments from users who owe money.

Introduces a dialog for inputting payment details (amount, method, description, reference), triggers an API call to record the transaction, and updates user balances and transaction history.

This is for non-lightning payments like cash, bank transfers, or checks.

views_api.py

@@ -59,6 +59,7 @@ from .models import (
     ReceivableEntry,
     RecordPayment,
     RevenueEntry,
+    SettleReceivable,
     UserBalance,
     UserWalletSettings,
 )
@@ -727,6 +728,116 @@ async def api_pay_user(
     }
 
 
+@castle_api_router.post("/api/v1/receivables/settle")
+async def api_settle_receivable(
+    data: SettleReceivable,
+    wallet: WalletTypeInfo = Depends(require_admin_key),
+) -> dict:
+    """
+    Manually settle a receivable (record when user pays castle in person).
+
+    This endpoint is for non-lightning payments like:
+    - Cash payments
+    - Bank transfers
+    - Other manual settlements
+
+    Admin only.
+    """
+    from lnbits.settings import settings as lnbits_settings
+
+    if wallet.wallet.user != lnbits_settings.super_user:
+        raise HTTPException(
+            status_code=HTTPStatus.FORBIDDEN,
+            detail="Only super user can settle receivables",
+        )
+
+    # Validate payment method
+    valid_methods = ["cash", "bank_transfer", "check", "other"]
+    if data.payment_method.lower() not in valid_methods:
+        raise HTTPException(
+            status_code=HTTPStatus.BAD_REQUEST,
+            detail=f"Invalid payment method. Must be one of: {', '.join(valid_methods)}",
+        )
+
+    # Get user's receivable account (what user owes)
+    user_receivable = await get_or_create_user_account(
+        data.user_id, AccountType.ASSET, "Accounts Receivable"
+    )
+
+    # Get the appropriate asset account based on payment method
+    payment_account_map = {
+        "cash": "Cash",
+        "bank_transfer": "Bank Account",
+        "check": "Bank Account",
+        "other": "Cash"
+    }
+
+    account_name = payment_account_map.get(data.payment_method.lower(), "Cash")
+    payment_account = await get_account_by_name(account_name)
+
+    # If account doesn't exist, try to find or create a generic one
+    if not payment_account:
+        # Try to find any asset account that's not receivable
+        all_accounts = await get_all_accounts()
+        for acc in all_accounts:
+            if acc.account_type == AccountType.ASSET and "receivable" not in acc.name.lower():
+                payment_account = acc
+                break
+
+    if not payment_account:
+        raise HTTPException(
+            status_code=HTTPStatus.NOT_FOUND,
+            detail=f"Payment account '{account_name}' not found. Please create it first.",
+        )
+
+    # Create journal entry
+    # DR Cash/Bank (asset increased), CR Accounts Receivable (asset decreased)
+    # This records that user paid their debt
+
+    # Add meta information for audit trail
+    entry_meta = {
+        "source": "manual_settlement",
+        "payment_method": data.payment_method,
+        "settled_by": wallet.wallet.user,
+        "payer_user_id": data.user_id,
+    }
+
+    entry_data = CreateJournalEntry(
+        description=data.description,
+        reference=data.reference or f"MANUAL-{data.user_id[:8]}",
+        flag=JournalEntryFlag.CLEARED,  # Manual payments are immediately cleared
+        meta=entry_meta,
+        lines=[
+            CreateEntryLine(
+                account_id=payment_account.id,
+                debit=data.amount,
+                credit=0,
+                description=f"Payment received via {data.payment_method}",
+            ),
+            CreateEntryLine(
+                account_id=user_receivable.id,
+                debit=0,
+                credit=data.amount,
+                description="Receivable settled",
+            ),
+        ],
+    )
+
+    entry = await create_journal_entry(entry_data, wallet.wallet.id)
+
+    # Get updated balance
+    balance = await get_user_balance(data.user_id)
+
+    return {
+        "journal_entry_id": entry.id,
+        "user_id": data.user_id,
+        "amount_settled": data.amount,
+        "payment_method": data.payment_method,
+        "new_balance": balance.balance,
+        "message": f"Receivable settled successfully via {data.payment_method}",
+    }
+
+
 # ===== SETTINGS ENDPOINTS =====