Fix onboarding UX and add replaceable journey analytics

Make recipient changes explicit, prioritize verification retry, and label simulated outcomes prominently. Add shared typed analytics with bounded dummy capture, correlated service events and documented PostHog adapter contract. Validate privacy, retries, abandonment, keyboard recovery and accessibility. Related to #12.

frontend/app/README.md

@@ -62,3 +62,12 @@ Use `context.goNamed(AppRoutes.… )` for top-level navigation. Existing hash UR
 The signup email travels as a transient route extra. The router's extra codec deliberately omits extras from serialized browser history, so a restored sent page asks for the email again. Do not add persistent route extras without explicitly updating that policy.
 
 These are public routes: no session or KYC guard is added to the dummy authentication flow. Future protected pages should use centralized redirects driven by authoritative session state, with backend access enforcement. Tracker: tech/sxchnge#6, branch `routing-6`.
+
+## UX and analytics
+
+The app accepts an optional `analyticsService` and defaults to the shared bounded
+in-memory dummy analytics sink. Semantic service events correlate signup, delivery
+and confirmation within this app instance. No analytics data leaves the device.
+See [the journey contract](../../docs/ux/auth-journeys.md) for the schema, metrics,
+PostHog adapter boundary and measurement limitations. Demo outcomes are explicitly
+simulated; recipient editing and internal-error recovery have dedicated controls.