feat: Prompt user to download model, if no models are available

[dan-menlo]

Problem

When there are no models available but user still has at least 1 old thread: - e.g. Factory reset (e.g. all models are deleted) - e.g. User deletes the /models folder from filesystem - e.g. User manually deletes all models - ...

Current behavior: We default a cloud model and show API key error, which is not cool.

Expected behavior: We should show that no model is available & recommend users to download one.

Design

• Should leverage existing Hub UX (minimal additional UX)
• Should be very gentle, avoid technical verbiage

Figma: https://www.figma.com/design/DYfpMhf8qiSReKvYooBgDV/Jan-App-(3rd-version)?node-id=8124-71826&t=af5Wyb9D89fwRirc-4

• When user tries to send a message -> show error: "You don’t have any available model." + Go to Hub button
• When user clicks on Model Menu to choose model -> recommend them 2 models from the Starter Screen (https://github.com/janhq/jan/issues/3170)

Tasklist

• [x] Designs @imtuyethan
• [ ] UI Implementation @urmauur

Related Issues

• #3385