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/windows/flutter/generated_plugin_registrant.cc

@@ -9,6 +9,7 @@
 #include <firebase_core/firebase_core_plugin_c_api.h>
 #include <flutter_secure_storage_windows/flutter_secure_storage_windows_plugin.h>
 #include <permission_handler_windows/permission_handler_windows_plugin.h>
+#include <url_launcher_windows/url_launcher_windows.h>
 
 void RegisterPlugins(flutter::PluginRegistry* registry) {
   FirebaseCorePluginCApiRegisterWithRegistrar(
@@ -17,4 +18,6 @@ void RegisterPlugins(flutter::PluginRegistry* registry) {
       registry->GetRegistrarForPlugin("FlutterSecureStorageWindowsPlugin"));
   PermissionHandlerWindowsPluginRegisterWithRegistrar(
       registry->GetRegistrarForPlugin("PermissionHandlerWindowsPlugin"));
+  UrlLauncherWindowsRegisterWithRegistrar(
+      registry->GetRegistrarForPlugin("UrlLauncherWindows"));
 }