feat: Allow users to favorite conversations from the left panel

[eckartal]

A feature for favorite conversations is in the left panel - a dedicated tab to display these favorites for quick access.

Implementation suggestions:

• Add a star icon next to each conversation in the left panel, which users can click to mark conversations as favorites.
• Favorites tab creation: Create a new tab within the main navigation area that filters and shows only the conversations marked as favs.

https://twitter.com/soyhenryxyz/status/1782820432531583477

[iamhenry]

🙏🏽

[imtuyethan]

I'll close as duplicated & make sure to include it in https://github.com/janhq/jan/issues/3133