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

[dan-homebrew]

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

[dan-homebrew]

Merging into https://github.com/janhq/jan/issues/3385

[dan-homebrew]

@imtuyethan I am moving this issue into Sprint 20, as @urmauur may be able to get to it this sprint.

• Can you reply to this thread with the Wireframes for the "no models" scenario?
• We can clear the designs async
• We can queue it for @urmauur next week, and schedule for v0.5.5 release

[imtuyethan]

^ Updated the description with new design @dan-homebrew

[dan-homebrew]

[imtuyethan]

Updated design: https://www.figma.com/design/DYfpMhf8qiSReKvYooBgDV/Jan-App-(3rd-version)?node-id=8124-71826&t=t7FOVtMEOSg7nFsJ-4

cc @dan-homebrew