Phase 3.5: Mitra Chat Request History (backend route + mitra app screens)

Replaces the home-screen pending-requests banner with a "Riwayat
Permintaan" CTA that opens a list of the mitra's last 20 chat requests
(any status). Pending rows pin to the top; non-pending rows open a
read-only detail screen with a "Lihat percakapan" CTA on accepted rows.

Backend:
- New service `getRecentRequestsForMitra(mitraId, { limit })` capped at
  20, pending pinned via `(response IS NULL AND status='pending_acceptance')
  DESC`. Customer call_name returned verbatim, with `'Anonim'` only as
  null-safety fallback (no anonymity-flag masking — see project memory).
- New route `GET /api/mitra/chat-requests/recent`. Strictly per-mitra
  scoped via the existing `resolveMitra` preHandler.

Mitra app:
- New `RequestResponse` enum in core/constants.dart.
- New Riverpod notifier `requestHistoryProvider` (AsyncValue<List<...>>,
  keepAlive) — pull-to-refresh + screen-mount fetch only, no WS.
- Two new screens (history list + detail) and two new GoRoutes.
- Home screen: `_PendingRequestsBanner` removed → `_RequestHistoryButton`
  Card with red count badge. Live count comes from the existing
  chatRequestProvider so nothing changes about the WS-driven badge math.

Plan + acceptance criteria in requirement/phase3.5-plan.md. flutter
analyze clean (zero new issues). Backend smoke-tested against real DB.
Real-device E2E pending.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

mitra_app/lib/core/chat/mitra_chat_notifier.g.dart

@@ -6,7 +6,7 @@ part of 'mitra_chat_notifier.dart';
 // RiverpodGenerator
 // **************************************************************************
 
-String _$mitraChatHash() => r'd5f4819264b9c71ce29a640ee2cfee608ead5e9e';
+String _$mitraChatHash() => r'da0c625b192c9ab24acd8ecc364b5f789c1ede41';
 
 /// See also [MitraChat].
 @ProviderFor(MitraChat)