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>

backend/src/services/mitra-activity.service.js

@@ -1,5 +1,5 @@
 import { getDb } from '../db/client.js'
-import { TopicSensitivity } from '../constants.js'
+import { SessionStatus, TopicSensitivity } from '../constants.js'
 
 const sql = getDb()
 
@@ -39,6 +39,30 @@ export const getMitraActivityLog = async ({ mitra_id, date_from, date_to, page =
   return { items, total: Number(count), page, limit }
 }
 
+export const getRecentRequestsForMitra = async (mitraId, { limit = 20 } = {}) => {
+  const cap = Math.min(Math.max(1, Number(limit) || 20), 20)
+  const items = await sql`
+    SELECT
+      crn.id              AS notification_id,
+      crn.session_id,
+      crn.notified_at,
+      crn.responded_at,
+      crn.response,
+      cs.status           AS session_status,
+      cs.topic_sensitivity,
+      COALESCE(NULLIF(trim(c.display_name), ''), 'Anonim') AS customer_call_name
+    FROM chat_request_notifications crn
+    LEFT JOIN chat_sessions cs ON cs.id = crn.session_id
+    LEFT JOIN customers c      ON c.id = cs.customer_id
+    WHERE crn.mitra_id = ${mitraId}
+    ORDER BY
+      (crn.response IS NULL AND cs.status = ${SessionStatus.PENDING_ACCEPTANCE}) DESC,
+      crn.notified_at DESC
+    LIMIT ${cap}
+  `
+  return items
+}
+
 export const getMitraActivitySummary = async ({ mitra_id, date_from, date_to } = {}) => {
   const conditions = []