[FE Offline Transfer] 1. Scaffold Vue App and basic route

What does this MR do and why?

Creates the route and basic app for /import/offline using feature flag offline_transfer_ui

The next ticket will include the other routes /export and /import, and controllers. As well as breadcrumbs, while implementing the Export flow

References

Figma https://www.figma.com/design/1uiBnqdUpMXV22OlpL7PAz/--581545--Offline-Transfer?node-id=4026-1077&t=muXB3oquRvzZpoiw-0

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Navigate to /import/offline . Should result in 404
2. In rails console Feature.enable(:offline_transfer_ui)
3. Navigate to /import/offline

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #586916 (closed)