v1 usability: improve onboarding for first-time setup and path configuration

[Nirandre]

Background

The current v1 release supports configurable paths, but the setup experience is still oriented toward technical users who are comfortable reading the README and configuring environment variables manually.

Goal

Make the first-run experience easier for new users.

Expected behavior

• The app should explain what the shared home is and what the account vault is.
• Users should be able to understand the defaults without reading source code.
• Path configuration should be easier to discover and validate.
• The app should provide clearer feedback if expected paths are missing or inaccessible.

Notes

This can still remain local-only and Windows-only.
A lightweight v1 improvement is enough; this does not need to become a full v2 setup wizard yet.