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/macos/Flutter/GeneratedPluginRegistrant.swift

@@ -5,6 +5,7 @@
 import FlutterMacOS
 import Foundation
 
+import firebase_analytics
 import firebase_core
 import firebase_messaging
 import flutter_local_notifications
@@ -17,6 +18,7 @@ import url_launcher_macos
 import webview_flutter_wkwebview
 
 func RegisterGeneratedPlugins(registry: FlutterPluginRegistry) {
+  FirebaseAnalyticsPlugin.register(with: registry.registrar(forPlugin: "FirebaseAnalyticsPlugin"))
   FLTFirebaseCorePlugin.register(with: registry.registrar(forPlugin: "FLTFirebaseCorePlugin"))
   FLTFirebaseMessagingPlugin.register(with: registry.registrar(forPlugin: "FLTFirebaseMessagingPlugin"))
   FlutterLocalNotificationsPlugin.register(with: registry.registrar(forPlugin: "FlutterLocalNotificationsPlugin"))