Backoffice stage 2: chats (support + concierge, files)

- ChatThread per client/provider and channel; messages get files, internal notes,
  source (bot/mini app) and delivery errors; reply templates. Migration moves old
  concierge messages into threads.
- Routing: subscribers write to the concierge, others to support; /support and
  /concierge in the client bot; staff can take, transfer, close and move threads.
- Telegram: photos/documents from clients and providers, replies with the channel
  header, files sent from storage, notifications only to the assignee or the
  channel's staff, "Reply" into a specific thread.
- New admin: /chats with list, conversation, notes, files, templates, client panel;
  "Message" button on the client card; dashboard counts threads awaiting reply.
- Client mini app: in-app chat screen sharing the same conversation.
- Old admin keeps working on the same data (notes hidden there).
- Tests for routing, notes, assign/close/move, lists, recipients; separate test DB
  via TEST_DB_NAME; dev:chats-demo script.

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

apps/api/src/routers/backoffice/index.ts

@@ -2,6 +2,7 @@ import { router } from '../../trpc.ts';
 import { boAuthRouter, boTeamRouter } from './auth.ts';
 import { boClientsRouter, boSegmentsRouter } from './clients.ts';
 import { boDashboardRouter } from './dashboard.ts';
+import { boChatsRouter } from './chats.ts';
 
 /** API новой админки (apps/backoffice) */
 export const backofficeRouter = router({
@@ -10,4 +11,5 @@ export const backofficeRouter = router({
   dashboard: boDashboardRouter,
   clients: boClientsRouter,
   segments: boSegmentsRouter,
+  chats: boChatsRouter,
 });