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/lib/generated/i18n/app_localizations_en.dart

@@ -201,7 +201,7 @@ class AppLocalizationsEn extends AppLocalizations {
   String get verificationRequest => 'Send a new verification email';
 
   @override
-  String get verificationRetry => 'Try again';
+  String get verificationRetry => 'Retry verification';
 
   @override
   String get verificationBack => 'Back to login';
@@ -219,4 +219,27 @@ class AppLocalizationsEn extends AppLocalizations {
 
   @override
   String get verificationStep => 'CONFIRM YOUR EMAIL';
+
+  @override
+  String get demoSentHeading => 'Demo email prepared.';
+
+  @override
+  String get demoSentBody =>
+      'No email was sent. Use the demo confirmation below to preview the next step.';
+
+  @override
+  String get demoVerifiedHeading => 'Demo verification\ncomplete.';
+
+  @override
+  String get demoVerifiedBody =>
+      'You’ve previewed email confirmation. No account was verified. Return to login to explore the demo.';
+
+  @override
+  String get verificationRecipient => 'Recipient';
+
+  @override
+  String get verificationChangeEmail => 'Change email';
+
+  @override
+  String get demoResend => 'Prepare demo email again';
 }