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/chat/screens/bestie_found_screen.dart

@@ -1,9 +1,11 @@
 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/chat/active_session_notifier.dart';
 import '../../../core/pairing/pairing_notifier.dart';
 import '../../../core/theme/halo_tokens.dart';
+import '../../payment/state/payment_draft_provider.dart';
 import '../../../core/theme/widgets/widgets.dart';
 
 /// Phase 4 Stage 5 — S9 Match-found screen.
@@ -35,6 +37,15 @@ class _BestieFoundScreenState extends ConsumerState<BestieFoundScreen> {
   @override
   void initState() {
     super.initState();
+    // Funnel step 12 — paired with a mitra. A targeted-mitra draft means the
+    // repeat funnel; otherwise activation. Fire once on view.
+    final isRepeat =
+        ref.read(paymentDraftNotifierProvider).targetedMitraId != null;
+    // ignore: discarded_futures
+    ref.read(analyticsProvider).logPairingMatched(
+          funnel:
+              isRepeat ? AnalyticsFunnel.repeat : AnalyticsFunnel.activation,
+        );
     ref.listenManual<PairingData>(pairingProvider, (prev, next) {
       if (!mounted) return;
       if (next is PairingActiveData) {