Beeper as an app option

I use [Beeper](https://www.beeper.com/) on a variety of platforms. Beeper's apps are mostly (all?) forks of [the Element reference implementations](https://github.com/element-hq/), so they should support most of the same functionality.

I'm not sure what would be involved in adding Beeper as an option here, even if it's "below the fold" (as an "experimental" app).

Does Beeper need to register an URL handler with the system, or something? According to [a comment on Reddit](https://www.reddit.com/r/beeper/comments/1bwm492/comment/l3c5ix1/?utm_source=share&utm_medium=web3x&utm_name=web3xcss&utm_term=1&utm_content=share_button) the URL handler for Beeper is `riot://`, but taking an `element://` link from matrix.to and replacing the `element://` with `riot://` doesn't work in Safari or Firefox on macOS.

(To be fair, matrix.to doesn't seem to want to open Element Desktop from Firefox for macOS, either, and instead prompts me to download Element Desktop or open the link in Element Web. The `element://` link does work properly in Safari, though.)

I can open a support ticket with Beeper, as well, and I will share a link to this issue with them.

Start by tracing matrix.to's URL handling and the existing app-option behavior described in the issue. Investigate whether Beeper's documented URL handler works across Safari and Firefox on macOS, and confirm what support would need to look like. Done means the issue has a defined implementation path and Beeper links open reliably where supported.

Written by the indexing model from the issue text.