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/core/chat/chat_notifier.g.dart

@@ -30,7 +30,7 @@ final chatRemainingSecondsProvider = AutoDisposeStreamProvider<int>.internal(
 @Deprecated('Will be removed in 3.0. Use Ref instead')
 // ignore: unused_element
 typedef ChatRemainingSecondsRef = AutoDisposeStreamProviderRef<int>;
-String _$chatHash() => r'a42bf404f5b38034c6c9511259b64b1092af3caa';
+String _$chatHash() => r'56f019ce6e527128ab42a71f56220c5412cfec0f';
 
 /// See also [Chat].
 @ProviderFor(Chat)

client_app/lib/core/chat/session_closure_notifier.g.dart

@@ -6,7 +6,7 @@ part of 'session_closure_notifier.dart';
 // RiverpodGenerator
 // **************************************************************************
 
-String _$sessionClosureHash() => r'a9aaf26da64d3489497d057e2b05741c08444e07';
+String _$sessionClosureHash() => r'1ab9df044138115e232b3df494e2895177d9d66d';
 
 /// See also [SessionClosure].
 @ProviderFor(SessionClosure)