Deliver localized auth app with verification and go_router

Integrate themed login/signup, EN/RU localization, shared dummy providers, verification recovery screens and named URL routes. Store frontend guidelines, workflow skills, validation and delivery documentation. Related to #2, #3, #5 and #6.

frontend/app/l10n.yaml

@@ -0,0 +1,5 @@
+arb-dir: lib/l10n
+output-dir: lib/generated/i18n
+template-arb-file: en.arb
+output-localization-file: app_localizations.dart
+untranslated-messages-file: untranslated.txt