Phase 4 §1/§5: notif banner detection on API <33 + chat-delivery WS→FCM lifecycle

§1 notif banner: permission_handler v11 returns granted unconditionally
for Permission.notification on Android <13 because POST_NOTIFICATIONS
didn't exist as a runtime permission. Result: SHome1st amber "notifikasi
off" banner never showed on API 24-32 even when the user toggled
notifications off in Settings → Apps. Add a
NotificationManagerCompat.areNotificationsEnabled() pre-check via
flutter_local_notifications (works from API 19+) so the banner reflects
the real OS state on older Android.

§5 chat delivery: the contract is "WS when foreground, FCM when
background", but the previous build only honoured (1) — Android keeps
the TCP socket alive after the Dart isolate is paused, so backend's
`socket.readyState === 1` check returned true and FCM never fired.
Fix has five parts (all required together):

 1. Customer-side lifecycle observer in client_app/main.dart closes
    chatProvider's WS on paused/detached, reconnects on resumed.
 2. `_appPaused` gate in main.dart suppresses the activeSessionProvider
    listener's auto-reconnect (15s poll in active_session_notifier
    would otherwise re-open the WS the next tick after the observer
    closed it — defeating the fallback).
 3. Mitra-side lifecycle observer in mitra_app/main.dart stashes
    `_pausedChatSessionId`, calls mitraChatProvider.disconnect(), and
    re-issues connect(saved) on resumed.
 4. MitraChat gains a `_connectedSessionId` field + getter so the
    observer in step 3 can read it back across disconnect (disconnect
    clears it; the next connect overwrites it).
 5. SearchingScreen resets pairingProvider when entering with a new
    draft.paymentId — previously it retained PairingActiveData with
    the *old* sessionId after a session ended, and the next pairing
    flow navigated straight to that completed session showing
    "Sesi sudah berakhir".

Backend additions under /internal/_test/* for assertion harness:
inspectSessionWsState + GET /ws-connection-state,
POST /send-chat-message-as-mitra (with delivered_via),
POST /send-chat-message-as-customer (with delivered_via),
POST /send-fcm-chat-message (raw FCM dispatch).

Maestro coverage:
 - ts-customer-05-01: mitra → customer message when customer is
   backgrounded → delivered_via=fcm.
 - ts-customer-05-02: customer → mitra message when mitra is
   backgrounded → delivered_via=fcm.
 - ts-customer-01-01: §1 notif-denied banner on home. Documented
   precondition: mitra must be force-stopped or backgrounded on the
   chat screen before 05-02 runs (Maestro can only drive one --udid
   per run; mitra-side lifecycle observer end-to-end is deferred).

Helper scripts under client_app/.maestro/scripts/:
inspect_ws_state.js, assert_ws_state.js,
send_chat_message_as_mitra.js, assert_delivered_via.js (takes
SENDER=mitra|customer to route to the matching backend endpoint).

README_section_05.md documents the test plan, helper scripts, and the
deferred mitra-side maestro driving. Both apps tested manually on
API 28 AVDs where FCM delivery is sub-second; API 24 has 5-30 min
heartbeats that make it impractical for FCM-related testing.

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

client_app/lib/core/notifications/notif_permission.dart

@@ -1,7 +1,9 @@
 import 'dart:async';
+import 'dart:io' show Platform;
 
 import 'package:firebase_messaging/firebase_messaging.dart';
 import 'package:flutter/widgets.dart';
+import 'package:flutter_local_notifications/flutter_local_notifications.dart';
 import 'package:permission_handler/permission_handler.dart' as ph;
 import 'package:riverpod_annotation/riverpod_annotation.dart';
 
@@ -14,11 +16,29 @@ enum NotifPermStatus { notDetermined, granted, denied }
 ///   - iOS uses Firebase Messaging (which surfaces the system UNNotification
 ///     authorization status).
 ///   - Android 13+ uses `permission_handler` for `Permission.notification`
-///     (POST_NOTIFICATIONS runtime). Older Android always reports granted.
+///     (POST_NOTIFICATIONS runtime).
+///   - Android <13: POST_NOTIFICATIONS doesn't exist as a runtime permission,
+///     so `permission_handler` returns `granted` regardless of the user's
+///     Settings → Apps → Notifications toggle. We add a
+///     `NotificationManagerCompat.areNotificationsEnabled()` pre-check via
+///     `flutter_local_notifications` to honour that user-facing toggle on
+///     older Android.
 class NotifPermission {
   const NotifPermission();
 
   Future<NotifPermStatus> readStatus() async {
+    // Older Android: permission_handler can't see the
+    // Settings → Apps → Notifications toggle, so we ask the local-notifs
+    // plugin (backed by NotificationManagerCompat.areNotificationsEnabled,
+    // which works from API 19). If disabled there, surface it as `denied`
+    // so the SHome1st banner reflects reality on API 24-32.
+    if (Platform.isAndroid) {
+      final androidImpl = FlutterLocalNotificationsPlugin()
+          .resolvePlatformSpecificImplementation<
+              AndroidFlutterLocalNotificationsPlugin>();
+      final enabled = await androidImpl?.areNotificationsEnabled();
+      if (enabled == false) return NotifPermStatus.denied;
+    }
     final phStatus = await ph.Permission.notification.status;
     return _mapPh(phStatus);
   }