Phase 4 Stage 4: notif gate + home permission-denied banner

Notif Gate full screen at /onboarding/notif-gate, reached from waiting
payment on confirmed/consumed status. Auto-advances to /chat/searching
when permission is already granted; otherwise shows izinkan/nanti aja
HaloButton CTAs. NotifPermission helper wraps firebase_messaging +
permission_handler with readStatus/request/openAppSettings; cached in
notifPermissionStatusProvider that re-reads on app foreground via an
internal WidgetsBindingObserver.

home_screen amber banner above-the-fold when notifPermissionStatusProvider
reports denied. Dismissable for the session via homeNotifBannerDismissedProvider
(in-memory StateProvider, no persistence - cold-restart re-shows).
nyalain CTA -> openAppSettings().

Manifest + Info.plist permission entries added.

Note: main.dart still pre-requests FirebaseMessaging permission at boot,
which can pre-resolve status so the gate auto-advances instead of acting
as the first prompt. Left intact for now; can be removed in a later
stage if the gate should be the first-ask UX.

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

client_app/lib/core/notifications/notif_permission.dart

@@ -0,0 +1,115 @@
+import 'dart:async';
+
+import 'package:firebase_messaging/firebase_messaging.dart';
+import 'package:flutter/widgets.dart';
+import 'package:permission_handler/permission_handler.dart' as ph;
+import 'package:riverpod_annotation/riverpod_annotation.dart';
+
+part 'notif_permission.g.dart';
+
+enum NotifPermStatus { notDetermined, granted, denied }
+
+/// Wraps `firebase_messaging` + `permission_handler` for the Phase 4 Stage 4
+/// notif gate. Reads/requests are platform-routed:
+///   - 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.
+class NotifPermission {
+  const NotifPermission();
+
+  Future<NotifPermStatus> readStatus() async {
+    final phStatus = await ph.Permission.notification.status;
+    return _mapPh(phStatus);
+  }
+
+  /// Shows the OS prompt only when status is [NotifPermStatus.notDetermined].
+  /// Otherwise returns the current status without re-prompting (the OS would
+  /// no-op anyway on a previously-resolved permission).
+  Future<NotifPermStatus> request() async {
+    final current = await readStatus();
+    if (current != NotifPermStatus.notDetermined) return current;
+
+    // Firebase Messaging requestPermission triggers the iOS prompt; on Android
+    // it is a no-op for permission UI but registers the FCM iOS APNS token.
+    // We still call permission_handler.request() so Android 13+ shows the
+    // POST_NOTIFICATIONS dialog.
+    await FirebaseMessaging.instance.requestPermission();
+    final phResult = await ph.Permission.notification.request();
+    return _mapPh(phResult);
+  }
+
+  Future<void> openAppSettings() => ph.openAppSettings();
+
+  NotifPermStatus _mapPh(ph.PermissionStatus s) {
+    if (s.isGranted || s.isLimited || s.isProvisional) {
+      return NotifPermStatus.granted;
+    }
+    if (s.isDenied) return NotifPermStatus.notDetermined;
+    // permanentlyDenied + restricted both behave like "denied — open settings".
+    return NotifPermStatus.denied;
+  }
+}
+
+final _helperProvider = Provider<NotifPermission>((_) => const NotifPermission());
+
+/// Cached notif permission status. Auto-refreshes on app foreground via an
+/// internal `WidgetsBindingObserver` — there is no shared `appLifecycleProvider`
+/// in this codebase yet, so the observer is owned here.
+@Riverpod(keepAlive: true)
+class NotifPermissionStatus extends _$NotifPermissionStatus {
+  _LifecycleHook? _hook;
+
+  @override
+  Future<NotifPermStatus> build() async {
+    _hook ??= _LifecycleHook(_onResumed);
+    ref.onDispose(() {
+      _hook?.detach();
+      _hook = null;
+    });
+    return ref.read(_helperProvider).readStatus();
+  }
+
+  /// Triggers the OS prompt (only if [NotifPermStatus.notDetermined]) and
+  /// re-publishes the resolved status.
+  Future<NotifPermStatus> request() async {
+    final result = await ref.read(_helperProvider).request();
+    state = AsyncData(result);
+    return result;
+  }
+
+  Future<void> openAppSettings() =>
+      ref.read(_helperProvider).openAppSettings();
+
+  /// Force a re-read — used after returning from app settings.
+  Future<void> refresh() async {
+    final s = await ref.read(_helperProvider).readStatus();
+    if (state.valueOrNull == s) return;
+    state = AsyncData(s);
+  }
+
+  void _onResumed() {
+    // Fire-and-forget; refresh is idempotent.
+    // ignore: unawaited_futures
+    refresh();
+  }
+}
+
+class _LifecycleHook with WidgetsBindingObserver {
+  _LifecycleHook(this._onResumed) {
+    WidgetsBinding.instance.addObserver(this);
+  }
+
+  final VoidCallback _onResumed;
+
+  void detach() {
+    WidgetsBinding.instance.removeObserver(this);
+  }
+
+  @override
+  void didChangeAppLifecycleState(AppLifecycleState state) {
+    if (state == AppLifecycleState.resumed) {
+      _onResumed();
+    }
+  }
+}

client_app/lib/core/notifications/notif_permission.g.dart

@@ -0,0 +1,31 @@
+// GENERATED CODE - DO NOT MODIFY BY HAND
+
+part of 'notif_permission.dart';
+
+// **************************************************************************
+// RiverpodGenerator
+// **************************************************************************
+
+String _$notifPermissionStatusHash() =>
+    r'16c81af5e48dab2c7d0cf33c985e0ca7c3d01006';
+
+/// Cached notif permission status. Auto-refreshes on app foreground via an
+/// internal `WidgetsBindingObserver` — there is no shared `appLifecycleProvider`
+/// in this codebase yet, so the observer is owned here.
+///
+/// Copied from [NotifPermissionStatus].
+@ProviderFor(NotifPermissionStatus)
+final notifPermissionStatusProvider =
+    AsyncNotifierProvider<NotifPermissionStatus, NotifPermStatus>.internal(
+  NotifPermissionStatus.new,
+  name: r'notifPermissionStatusProvider',
+  debugGetCreateSourceHash: const bool.fromEnvironment('dart.vm.product')
+      ? null
+      : _$notifPermissionStatusHash,
+  dependencies: null,
+  allTransitiveDependencies: null,
+);
+
+typedef _$NotifPermissionStatus = AsyncNotifier<NotifPermStatus>;
+// ignore_for_file: type=lint
+// ignore_for_file: subtype_of_sealed_class, invalid_use_of_internal_member, invalid_use_of_visible_for_testing_member, deprecated_member_use_from_same_package