Phase 4 Stage 8: returning-user shell + Tanya Admin sheet

Bestie Choice Sheet on home Mulai Curhat CTA. When the user has at
least one prior session (bestieHistoryHasItemsProvider hits the chat-
sessions history endpoint), the CTA opens a HaloBottomSheet with two
cards: 'bestie yang udah kenal' -> /chat/history, 'bestie baru' ->
/payment/entry. Empty history -> direct to /payment/entry.

Bestie history list visual upgrade: HaloOrb (mitraId seed) + name +
last-session date + topic pills + sessions count + ONLINE pill.
Backend getCustomerHistory now returns topics, mitra_is_online,
sessions_count in a single payload (no per-row presence round-trip).

BestieOfflinePopup with two variants (returning | new_) replacing the
legacy BestieUnavailableDialog. tanya admin ghost CTA on both variants
opens the new TanyaAdminSheet. Stage 5's targeted-wait declined stub
+ Stage 7's chat-screen 409 stub + searching-screen call site all
migrated to the real component.

TanyaAdminSheet: HaloBottomSheet with WA + Telegram buttons, deeplinks
fetched via supportHandlesProvider (CC-config-driven). url_launcher
added to client_app; ios LSApplicationQueriesSchemes covers
https/http/whatsapp/tg.

Stage 2's OTP-blocked popup hubungi admin SnackBar stub also migrated
to TanyaAdminSheet.

Dev-only POST /internal/_test/seed-history-session lets Maestro 08
flow seed a history row before exercising the choice sheet.

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

client_app/lib/features/chat/screens/chat_screen.dart

@@ -8,8 +8,8 @@ import '../../../core/chat/session_closure_notifier.dart';
 import '../../../core/config/app_config_provider.dart';
 import '../../../core/constants.dart';
 import '../../../core/theme/halo_tokens.dart';
-import '../../../core/theme/widgets/halo_popup.dart';
 import '../../../core/theme/widgets/halo_snackbar.dart';
+import '../widgets/bestie_unavailable_dialog.dart';
 import '../widgets/chat_expired_banner.dart';
 import '../widgets/closing_message_sheet.dart';
 import '../widgets/confirm_end_step1.dart';
@@ -169,13 +169,10 @@ class _ChatScreenState extends ConsumerState<ChatScreen> {
     if (_rejectPopupShown) return;
     _rejectPopupShown = true;
     if (!mounted) return;
-    // TODO(stage8): replace with BestieOfflinePopup variant: 'returning'
-    await HaloPopup.show<void>(
+    await BestieOfflinePopup.show(
       context,
-      title: 'bestie lagi balik...',
-      body: 'sesi belum bisa ditutup karena bestie masih nyaut. coba lagi sebentar ya.',
-      icon: const Text('🔄', style: TextStyle(fontSize: 40)),
-      primary: HaloPopupAction(label: 'oke', onPressed: () {}),
+      variant: BestieOfflineVariant.returning,
+      mitraName: widget.mitraName,
     );
     _rejectPopupShown = false;
     // Reset closure state so the user can retry without a stale-error block.