viewing a (non-Shoot) user's outbox

This is perhaps a bit of scope creep, but it would be nice to be able to view non-Shoot objects in a simple timeline-like view on a user's profile. Some work was put into this via https://github.com/MaddyUnderStars/shoot/tree/feat/view_fed_outbox

Some considerations:
- Wrangle them into Shoot chat messages. Make the user's outbox a channel?

What would the message format be? Embeds/URL previews will come eventually, I could expand that to be like Discord's embeds (e.g. 'Rich messages" with an embed format that supports images, video, footers, etc). Bit much perhaps.

Alternatively, the external content could just be converted to a message with a good attempt, i.e. quote posts become links to the other content which embeds as normal, or peertube videos become links which embed as normal, etc.

- Create a new database table for external non-Shoot content?

doing this keeps the content in the most well preserved state but it's probably not the best option for maintainability? I'd just rather not have a bunch of random tables that aren't for Shoot's own content.

- I'd love to copy the UI of https://github.com/Nerimity/nerimity-web here, I think they do this well.

Start by reviewing the existing feat/view_fed_outbox branch and the referenced Nerimity web UI. Before implementation, determine the content representation, storage approach, message format, and profile timeline behavior; the work is done when those choices are settled and the resulting view is specified end to end.

Written by the indexing model from the issue text.