feat(client/analytics): GA4 funnel instrumentation + unified home CTA

Add Firebase Analytics (GA4) funnel tracking to client_app:
- AnalyticsService typed wrapper (enum-gated, no PII) + analyticsProvider
- FirebaseAnalyticsObserver on GoRouter (screen_name via nameExtractor)
- user_id = customer UUID, user_type property, set on auth resolve/upgrade
- funnel events: curhat_start, curhat_repeat_start, auth_*, onboarding_usp_view,
  payment_view, payment_method_select, payment_started, pairing_matched/no_bestie
- bottom-sheet events: verif_choice_view/select, bestie_choice_view/select,
  extension_offer_view, chat_extension_requested
- payment_started carries app_instance_id + ga_session_id in the
  /payment-requests body for future server-side stitching (backend ignores)
- curhat_mode_pick screen name disambiguates the chat/call mode picker
  (/payment/method-pick) from the payment-channel picker (/payment/method)
- unify both home CTAs to "Aku Mau Curhat"

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

client_app/lib/features/home/widgets/bestie_choice_sheet.dart

@@ -1,6 +1,7 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:go_router/go_router.dart';
+import '../../../core/analytics/analytics_service.dart';
 import '../../../core/theme/halo_tokens.dart';
 import '../../../core/theme/widgets/widgets.dart';
 import '../../payment/state/payment_draft_provider.dart';
@@ -52,6 +53,8 @@ class BestieChoiceSheet extends ConsumerWidget {
           subtitle: 'lanjut cerita ke bestie yang pernah dengerin kamu.',
           icon: Icons.favorite_outline,
           onTap: () {
+            // ignore: discarded_futures
+            ref.read(analyticsProvider).logBestieChoiceSelect(knownBestie: true);
             Navigator.of(context).pop();
             context.push('/bestie/history');
           },
@@ -62,6 +65,8 @@ class BestieChoiceSheet extends ConsumerWidget {
           subtitle: 'cari bestie baru yang siap dengerin sekarang.',
           icon: Icons.auto_awesome_outlined,
           onTap: () {
+            // ignore: discarded_futures
+            ref.read(analyticsProvider).logBestieChoiceSelect(knownBestie: false);
             // explicit reset — this branch is blast-only, clear any stale targeted mitra
             ref.read(paymentDraftNotifierProvider.notifier).reset();
             Navigator.of(context).pop();