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/no_bestie_screen.dart

@@ -1,7 +1,9 @@
 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/pairing/pairing_notifier.dart';
+import '../../payment/state/payment_draft_provider.dart';
 
 /// Terminal failed-pairing screen.
 ///
@@ -13,11 +15,30 @@ import '../../../core/pairing/pairing_notifier.dart';
 /// Single CTA "Kembali ke beranda" resets the pairing notifier and routes
 /// home. PopScope falls back to home for deep-link entry per project memory
 /// rule "Deep-link pop fallback".
-class NoBestieScreen extends ConsumerWidget {
+class NoBestieScreen extends ConsumerStatefulWidget {
   const NoBestieScreen({super.key});
 
   @override
-  Widget build(BuildContext context, WidgetRef ref) {
+  ConsumerState<NoBestieScreen> createState() => _NoBestieScreenState();
+}
+
+class _NoBestieScreenState extends ConsumerState<NoBestieScreen> {
+  @override
+  void initState() {
+    super.initState();
+    // Funnel drop-off marker — pairing failed. 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).logPairingNoBestie(
+          funnel:
+              isRepeat ? AnalyticsFunnel.repeat : AnalyticsFunnel.activation,
+        );
+  }
+
+  @override
+  Widget build(BuildContext context) {
     return PopScope(
       canPop: true,
       onPopInvokedWithResult: (didPop, _) {