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/payment/screens/payment_entry_screen.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/auth/onboarding_intent_provider.dart';
 import '../../../core/chat/chat_opening_provider.dart';
 import '../../../core/theme/halo_tokens.dart';
@@ -38,6 +39,18 @@ class _PaymentEntryScreenState extends ConsumerState<PaymentEntryScreen> {
       // inherit a stale onboarding intent.
       ref.read(onboardingIntentProvider.notifier).state =
           OnboardingIntent.recover;
+
+      // Funnel step 8 — payment entry. A targeted mitra (set just before this
+      // screen by the bestie-history list) marks the repeat funnel; otherwise
+      // it's activation. resetExceptTarget() above preserves that flag.
+      final isRepeat =
+          ref.read(paymentDraftNotifierProvider).targetedMitraId != null;
+      // ignore: discarded_futures
+      ref.read(analyticsProvider).logPaymentView(
+            funnel:
+                isRepeat ? AnalyticsFunnel.repeat : AnalyticsFunnel.activation,
+            isRepeat: isRepeat,
+          );
     });
   }