Chats: show which order a provider writes about, or that there is no order

- Provider messages store the order that was current when they wrote: a started
  order first, otherwise the nearest assigned one within -4h..+12h; none — "no order".
- Admin chat: order tag above each provider message, "now / next" order strip in
  the conversation header, order number (or "no order") in the thread list.
- Telegram notification to the team gets an order line or "no current order".
- Test for the order-picking rule; demo shows both cases.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

packages/db/prisma/schema.prisma

@@ -465,6 +465,7 @@ model Order {
   offers     OrderOffer[]
   files      OrderFile[]
   messages   Message[]
+  chatMessages ConciergeMessage[]
   estimates  Estimate[]
   rating     Rating?
   lessons    LessonPackage?
@@ -1152,6 +1153,9 @@ model ConciergeMessage {
   size        Int?
   /// не удалось доставить в Telegram (клиент заблокировал бота и т.п.)
   deliveryError String?
+  /// исполнитель писал по этому заказу (текущий заказ в момент сообщения); null — заказа тогда не было
+  orderId     String?
+  order       Order?          @relation(fields: [orderId], references: [id], onDelete: SetNull)
   /// оператор прочитал сообщение клиента
   readAt      DateTime?
   createdAt   DateTime        @default(now())