Show more actionable message when user has no project permissions instead of "Oops"

### Is your feature request related to a problem?

Summary

When a user is added to an organisation but has no project-level permissions, the UI displays a generic "Oops" error. This should instead show a meaningful message indicating they don't have access to any projects and should contact their org admin.

Current Behavior

A user who successfully joins an organisation but has not been granted access to any projects sees a generic "Oops" page with no explanation.

### Describe the solution you'd like.

The UI should detect that the user has org membership but no project permissions, and display a message like "You don't have access to any projects yet. Contact your organisation admin to get access."

### Describe alternatives you've considered

Don't show an error at all. Show the dashboard with an empty state like "No projects available contact your admin for access."

### Additional context

Edge cases to address:

- Organizations with no projects at all
- Don't show the "contact administrator" message to organization admins themselves (since they *are* the administrators)