Add pending chat requests CTA on mitra home screen

- Backend: new GET /api/mitra/chat-requests/pending endpoint
- Backend: getPendingRequestsForMitra() queries unresponded notifications
  for sessions still in pending_acceptance status
- Mitra app: loadPendingRequests() fetches on screen load + status toggle
- Mitra app: activeRequestCount getter exposes queue size
- Mitra app: _PendingRequestsBanner widget shows count with tap-to-view

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/src/services/pairing.service.js

@@ -307,6 +307,19 @@ export const expirePairingRequest = async (sessionId) => {
   return session
 }
 
+export const getPendingRequestsForMitra = async (mitraId) => {
+  const rows = await sql`
+    SELECT cs.id AS session_id, cs.duration_minutes, cs.is_free_trial, cs.created_at
+    FROM chat_request_notifications crn
+    JOIN chat_sessions cs ON cs.id = crn.session_id
+    WHERE crn.mitra_id = ${mitraId}
+      AND crn.response IS NULL
+      AND cs.status = ${SessionStatus.PENDING_ACCEPTANCE}
+    ORDER BY cs.created_at ASC
+  `
+  return rows
+}
+
 export const getSessionStatus = async (sessionId) => {
   const [session] = await sql`
     SELECT cs.id, cs.customer_id, cs.mitra_id, cs.status, cs.created_at, cs.paired_at, cs.ended_at, cs.ended_by,