Incorporate more activity into homepage feed

- New members (maybe chunked together)
- New projects (maybe chunked together)
- Concluded meetups with a list of all who checked in

This should probably start as a wireframe that explores how to lay all this out with the existing content cleanly. It might be cool to include or preview commenting on some or all of these items right from the feed.

Start by reviewing the homepage feed and how its existing content is laid out. Create a wireframe exploring grouped new members, grouped new projects, and concluded meetups with check-in lists, while considering where optional feed commenting could fit. Done means the proposed layout is documented clearly enough to evaluate.

Written by the indexing model from the issue text.