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.spec.ts

@@ -0,0 +1,50 @@
+import { Prisma } from '@prisma/client';
+import { OrdersService } from './orders.service';
+
+/**
+ * Owner ruling 2026-10-08: an order is credited to the customer's expert AT
+ * THE MOMENT IT IS PLACED (legacy `orders.reagent_id`), and a later change of
+ * the customer's expert never moves it.
+ */
+describe('OrdersService.createOrder — sales expert credit', () => {
+  function build(referredByAgentId: string | null) {
+    const created: Record<string, unknown>[] = [];
+    const tx = {
+      order: {
+        create: jest.fn(async ({ data }: { data: Record<string, unknown> }) => {
+          created.push(data);
+          return { id: 'o1', ...data };
+        }),
+      },
+    };
+    const prisma = {
+      customer: {
+        findUnique: jest.fn(async () => ({
+          id: 'c1',
+          referredByAgentId,
+          goldDebtGrams: new Prisma.Decimal(0),
+          goldCreditLimitGrams: new Prisma.Decimal(1000),
+        })),
+      },
+      $transaction: jest.fn(async (fn: (t: typeof tx) => unknown) => fn(tx)),
+    };
+    const catalog = { getVariantOrThrow: jest.fn(async () => ({ id: 'v1', rashWeightGrams: '10' })) };
+    const accounting = { orderStatusReached: jest.fn() };
+    const service = new OrdersService(prisma as never, catalog as never, {} as never, accounting as never);
+    return { service, created };
+  }
+
+  const dto = { items: [{ productVariantId: 'v1', quantity: 1, wagePercent: 3 }] } as never;
+
+  it("records the customer's current expert on the order", async () => {
+    const { service, created } = build('agent-A');
+    await service.createOrder(dto, 'c1');
+    expect(created[0].salesAgentId).toBe('agent-A');
+  });
+
+  it('records no expert for a customer without one', async () => {
+    const { service, created } = build(null);
+    await service.createOrder(dto, 'c1');
+    expect(created[0].salesAgentId).toBeNull();
+  });
+});