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.

docs/implementation.md

@@ -106,3 +106,14 @@ Delivery validation passed: 56 frontend tests; formatting and all four Flutter
 analyses; 3 website tests, Astro check (zero errors/warnings), and website build.
 The app web build and browser checks passed during the immediately preceding
 routing task; delivery changed documentation and Git organization only.
+
+## Onboarding UX fixes and analytics preparation
+
+Task [#12](https://git.sendico.io/tech/sxchnge/issues/12) corrects the four UX
+review findings: measurable submitted journeys, accurate sent recipient state,
+primary retry on confirmation errors, and prominent/truthful simulated outcomes.
+The new shared `sxchnge_analytics` package supplies typed events, a bounded dummy
+sink and a journey recorder; auth service decorators keep collection independent
+of widgets. A PostHog adapter can replace the sink later; no actual SDK or data
+transmission is included. The [journey contract](ux/auth-journeys.md) records event
+semantics, metrics, privacy constraints, windows, validation and limitations.