feat: add billFwdStatus auto-trigger for when-payed strategy

Enables automatic email notification trigger when all bills are marked as paid
under "when-payed" forwarding strategy. Complements the existing "when-attached"
strategy to support both notification workflows.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

web-app/app/lib/actions/billActions.ts

@@ -79,7 +79,7 @@ const FormSchema = (t: IntlTemplateFn) => z.object({
  * @param hasNewAttachment - Whether a new attachment is being added
  * @returns true if billFwdStatus should be set to "pending"
  */
-const shouldUpdateBillFwdStatus = (
+const shouldUpdateBillFwdStatusWhenAttached = (
     location: BillingLocation,
     currentBillId: string | undefined,
     hasNewAttachment: boolean
@@ -111,6 +111,45 @@ const shouldUpdateBillFwdStatus = (
     return allOtherBillsHaveAttachments;
 };
 
+/**
+ * Checks if billFwdStatus should be updated to "pending" based on paid status
+ * @param location - The billing location containing the bill
+ * @param currentBillId - The ID of the bill being updated (to exclude from check)
+ * @param isPaid - Whether the current bill is being marked as paid
+ * @returns true if billFwdStatus should be set to "pending"
+ */
+const shouldUpdateBillFwdStatusWhenPayed = (
+    location: BillingLocation,
+    currentBillId: string | undefined,
+    isPaid: boolean
+): boolean => {
+    // Only proceed if the bill is being marked as paid
+    if (!isPaid) {
+        return false;
+    }
+
+    // Check billFwdEnabled is true
+    if (location.billFwdEnabled !== true) {
+        return false;
+    }
+
+    // Check billFwdStrategy is "when-payed"
+    if (location.billFwdStrategy !== "when-payed") {
+        return false;
+    }
+
+    // Check billFwdStatus is null or "failed"
+    if (location.billFwdStatus !== null && location.billFwdStatus !== "failed") {
+        return false;
+    }
+
+    // Check if ALL other bills are paid
+    const otherBills = location.bills.filter(bill => bill._id !== currentBillId);
+    const allOtherBillsPaid = otherBills.every(bill => bill.paid === true);
+
+    return allOtherBillsPaid;
+};
+
 /**
  * converts the file to a format stored in the database
  * @param billAttachment
@@ -227,7 +266,9 @@ export const updateOrAddBill = withUser(async (user: AuthenticatedUser, location
     }
 
     // Check if we should update billFwdStatus to "pending"
-    const shouldSetFwdPending = shouldUpdateBillFwdStatus(location, billId, billAttachment !== null);
+    const shouldSetFwdPendingWhenAttached = shouldUpdateBillFwdStatusWhenAttached(location, billId, billAttachment !== null);
+    const shouldSetFwdPendingWhenPayed = shouldUpdateBillFwdStatusWhenPayed(location, billId, billPaid);
+    const shouldSetFwdPending = shouldSetFwdPendingWhenAttached || shouldSetFwdPendingWhenPayed;
 
     if (billId) {