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/screens/bestie_history_list_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/constants.dart';
 import '../../../core/theme/halo_tokens.dart';
 import '../../../core/theme/widgets/widgets.dart';
@@ -132,6 +133,13 @@ class BestieHistoryListScreen extends ConsumerWidget {
                       return;
                     }
                     if (item.mitraId == null) return;
+                    // Repeat funnel: user re-selected a known bestie. mitra_ref
+                    // is opaque (hashed) — never the raw mitra id, per the
+                    // no-PII / opaque-mitra-identity rule.
+                    // ignore: discarded_futures
+                    ref.read(analyticsProvider).logBestieReselect(
+                          mitraRef: item.mitraId!.hashCode.toString(),
+                        );
                     // Stamp the targeted mitra onto the payment draft; the
                     // multi-screen payment flow (entry → method → waiting →
                     // notif-gate → searching) reads it back to fire the