feat(orders): credit each order to the expert who placed it, as legacy did

Legacy fixed `orders.reagent_id` once, when the order was placed, and its
«میزان فروش» summed `customer_id = X OR reagent_id = X`. The app credited
orders to the customer's CURRENT referrer and left out an expert's own
orders, so 9 of 49 imported experts showed a different figure.

- Order.salesAgentId (+ referrerCustomerId for 17 legacy orders whose
  referrer was not an expert); additive migration, recent app orders
  backfilled from the customer's referrer
- createOrder records the expert at placement time
- one shared filter (agent-orders.ts) for the experts list, expert
  detail, dashboard and the expert app; child orders follow salesAgentId
- customer page gets its «میزان فروش» back
- import carries orders.reagent_id as is; ex-experts kept as admins keep
  their profile so their own orders stay linked
- reconcile-sales: 1,557 of 1,558 match legacy's own formula; balances
  unchanged

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/api/src/modules/orders/orders.service.ts

@@ -105,6 +105,11 @@ export class OrdersService {
           wageWeightGrams,
           flatRialCharge,
           isSuspendedOverCreditLimit,
+          // Legacy `'reagent_id' => auth()->user()->reagent_id`
+          // (ApiMobileController.php:601): the customer's expert at THIS
+          // moment, fixed on the order so a later change of expert never moves
+          // past sales (owner ruling 2026-10-08).
+          salesAgentId: customer.referredByAgentId,
           items: {
             create: computedItems.map((item) => ({
               productVariantId: item.productVariantId,