feat: add favorite activities UI to activity library

[nickoferrall]

Fix #9114

Demo: https://www.loom.com/share/9250b4b5414a4318a67aaf29a6a222cb

This PR won't be merged until the functionality is added in a subsequent PR.

To test

• See the favourite icon in the activity library card
• See that it only appears in the grid view
• Clicking the favourite icon changes the colour. It becomes red
• The heart emoji tab in the activity library is red and changes to white when active
• Empty state looks like the design (I didn't include the "Your Favourite" title in the empty state as I didn't think it's needed)

[nickoferrall]

Hey @ackernaut, would you mind reviewing the UI for this one, please?

[ackernaut]

The UI looks great, nice work Nick!