Fix retroactive wizard: never set paid_amount for non-paid status

The elseif branch accepted form's paid_amount even when status was
'overdue', causing paid_amount to equal total_amount without a payment
record. This made fine calculator see unpaid=0 and skip the year.

Now only status='paid' sets paid_amount; all other statuses get 0.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/Modules/Members/Services/RetroactiveMembershipService.php

@@ -660,12 +660,10 @@ final class RetroactiveMembershipService
         // total_amount = base - discount (dev fee is separate, added at invoice level)
         $totalAmount = bcsub($baseAmount, $discountAmount, 2);
 
-        // For paid status: paid_amount = total (dev fee is invoice-level, not per-row paid)
+        // paid_amount only set when status is actually paid
         $paidAmount = '0.00';
         if ($status === 'paid') {
             $paidAmount = $totalAmount;
-        } elseif (isset($sub['paid_amount']) && bccomp((string) $sub['paid_amount'], '0', 2) > 0) {
-            $paidAmount = (string) $sub['paid_amount'];
         }
 
         $paymentId = null;