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/pubspec.lock

@@ -297,6 +297,30 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "7.0.1"
+  firebase_analytics:
+    dependency: "direct main"
+    description:
+      name: firebase_analytics
+      sha256: "4f85b161772e1d54a66893ef131c0a44bd9e552efa78b33d5f4f60d2caa5c8a3"
+      url: "https://pub.dev"
+    source: hosted
+    version: "11.6.0"
+  firebase_analytics_platform_interface:
+    dependency: transitive
+    description:
+      name: firebase_analytics_platform_interface
+      sha256: a44b6d1155ed5cae7641e3de7163111cfd9f6f6c954ca916dc6a3bdfa86bf845
+      url: "https://pub.dev"
+    source: hosted
+    version: "4.4.3"
+  firebase_analytics_web:
+    dependency: transitive
+    description:
+      name: firebase_analytics_web
+      sha256: c7d1ed1f86ae64215757518af5576ff88341c8ce5741988c05cc3b2e07b0b273
+      url: "https://pub.dev"
+    source: hosted
+    version: "0.5.10+16"
   firebase_core:
     dependency: "direct main"
     description: