Notify requester distinctly when receiver cancels their claimed order (Task #67)

Context
- After Task #64 receivers can cancel an order they have already claimed.
- Previously the requester's cancellation notification body was the same regardless of who cancelled (admin vs receiver), giving them no signal that their order had been claimed and then dropped.

Changes
- artifacts/api-server/src/routes/service-orders.ts (PATCH /orders/:id/status, cancel branch):
  - When the cancellation is initiated by the order's currently assigned receiver
    (existing.assignedTo === userId && next === "cancelled"), the requester's
    notification body now includes the bilingual phrase
    "استلم طلبك ولكن تم إلغاؤه لاحقاً" / "Your order was claimed but later
    cancelled by the receiver", appended to the service name for context.
  - Admin / non-assignee cancellations keep the existing service-name body so
    the two cases remain distinguishable in the requester's notifications list.
  - The notification is created via the existing notifyUser() helper, which
    persists to notifications and emits notification_created over Socket.IO,
    so the bell badge updates in real time.
- artifacts/api-server/tests/service-orders.test.mjs:
  - Added "requester gets a distinct notification when the receiver cancels a
    claimed order" covering the full flow: place → confirm-receipt → cancel,
    then asserts the owner has a cancellation notification whose body matches
    the new bilingual receiver-cancel copy.

Verification
- All 7 tests in service-orders.test.mjs pass locally against the running API.

Notes / deviations
- Locale JSON files (ar.json/en.json) were inspected but not modified: notification
  copy is stored server-side as titleAr/titleEn/bodyAr/bodyEn on the notifications
  row; the client just renders those strings directly.

Replit-Task-Id: 5aa480a9-c6e0-4a06-8919-b2b6784d8a98

artifacts/api-server/src/routes/service-orders.ts

@@ -348,12 +348,19 @@ router.patch(
         cancelled: ["تم إلغاء طلبك", "Your order was cancelled"],
       };
       const [titleAr, titleEn] = titleMap[next];
+      let bodyAr = enriched.service.nameAr;
+      let bodyEn = enriched.service.nameEn;
+      // Distinguish receiver-initiated cancel from admin-initiated cancel
+      if (next === "cancelled" && existing.assignedTo === userId) {
+        bodyAr = `${enriched.service.nameAr} — استلم طلبك ولكن تم إلغاؤه لاحقاً`;
+        bodyEn = `${enriched.service.nameEn} — Your order was claimed but later cancelled by the receiver`;
+      }
       await notifyUser(
         enriched.userId,
         titleAr,
         titleEn,
-        enriched.service.nameAr,
-        enriched.service.nameEn,
+        bodyAr,
+        bodyEn,
         orderId,
       );
     }

artifacts/api-server/tests/service-orders.test.mjs

@@ -259,6 +259,44 @@ test("status transitions matrix: receiver flows + owner/admin cancel rules", asy
   assert.equal((await res.json()).status, "cancelled");
 });
 
+test("requester gets a distinct notification when the receiver cancels a claimed order", async () => {
+  const owner = await createUser("ownN", "user");
+  const recv = await createUser("recvN", "order_receiver");
+  const co = await login(owner.username);
+  const cr = await login(recv.username);
+
+  let res = await call(co, "POST", "/orders", { serviceId });
+  assert.equal(res.status, 201);
+  const order = await res.json();
+  createdOrderIds.push(order.id);
+
+  // Receiver claims, then cancels
+  res = await call(cr, "PATCH", `/orders/${order.id}/confirm-receipt`);
+  assert.equal(res.status, 200);
+  res = await call(cr, "PATCH", `/orders/${order.id}/status`, {
+    status: "cancelled",
+  });
+  assert.equal(res.status, 200);
+
+  // Owner should have a cancellation notification with the receiver-cancel body
+  const { rows } = await pool.query(
+    `SELECT title_ar, title_en, body_ar, body_en
+       FROM notifications
+      WHERE user_id = $1 AND related_type = 'order' AND related_id = $2
+      ORDER BY id DESC`,
+    [owner.id, order.id],
+  );
+  const cancelNotif = rows.find(
+    (n) => n.title_en === "Your order was cancelled",
+  );
+  assert.ok(cancelNotif, "expected a cancellation notification for the owner");
+  assert.match(
+    cancelNotif.body_en,
+    /claimed but later cancelled by the receiver/,
+  );
+  assert.match(cancelNotif.body_ar, /استلم طلبك ولكن تم إلغاؤه لاحقاً/);
+});
+
 test("unauthenticated cannot place order", async () => {
   const res = await fetch(`${API_BASE}/api/orders`, {
     method: "POST",