Enables manual settlement with fiat currencies

Adds support for settling receivables with fiat currencies
like EUR and USD, in addition to sats.

Updates the settlement dialog to handle fiat amounts and
exchange rates, defaulting to cash payment when a fiat balance
exists.

Modifies the API to accept currency and amount_sats parameters
and adjust the journal entry accordingly, converting the fiat amount
to minor units (e.g., cents) for accounting purposes.

views_api.py

@@ -826,6 +826,26 @@ async def api_settle_receivable(
     # DR Cash/Bank (asset increased), CR Accounts Receivable (asset decreased)
     # This records that user paid their debt
 
+    # Convert amount to sats (minor units)
+    # For fiat currencies, store as cents/minor units
+    # For satoshis, just convert to int
+    from decimal import Decimal
+
+    if data.currency:
+        # Fiat currency payment (e.g., EUR, USD)
+        amount_minor_units = int(data.amount * 100)  # Convert to cents
+        line_metadata = {
+            "fiat_currency": data.currency,
+            "fiat_amount": str(data.amount),
+        }
+        if data.amount_sats:
+            line_metadata["sats_equivalent"] = data.amount_sats
+            line_metadata["exchange_rate"] = data.amount_sats / float(data.amount)
+    else:
+        # Satoshi payment
+        amount_minor_units = int(data.amount)
+        line_metadata = {}
+
     # Add meta information for audit trail
     entry_meta = {
         "source": "manual_settlement",
@@ -833,6 +853,8 @@ async def api_settle_receivable(
         "settled_by": wallet.wallet.user,
         "payer_user_id": data.user_id,
     }
+    if data.currency:
+        entry_meta["currency"] = data.currency
 
     entry_data = CreateJournalEntry(
         description=data.description,
@@ -842,15 +864,17 @@ async def api_settle_receivable(
         lines=[
             CreateEntryLine(
                 account_id=payment_account.id,
-                debit=data.amount,
+                debit=amount_minor_units,
                 credit=0,
                 description=f"Payment received via {data.payment_method}",
+                metadata=line_metadata,
             ),
             CreateEntryLine(
                 account_id=user_receivable.id,
                 debit=0,
-                credit=data.amount,
+                credit=amount_minor_units,
                 description="Receivable settled",
+                metadata=line_metadata,
             ),
         ],
     )
@@ -863,7 +887,8 @@ async def api_settle_receivable(
     return {
         "journal_entry_id": entry.id,
         "user_id": data.user_id,
-        "amount_settled": data.amount,
+        "amount_settled": float(data.amount),
+        "currency": data.currency,
         "payment_method": data.payment_method,
         "new_balance": balance.balance,
         "message": f"Receivable settled successfully via {data.payment_method}",