content: Distinguish direct and wildcard mentions

[chrisbobbe]

Currently, we don't distinguish the appearance of direct mentions and wildcard mentions:

The web app does that—

—and we should too, probably using the same colors web does.

I'll file a separate issue for a related but different feature: highlighting non-silent mentions of the self-user. That will take more data-model thinking. -> #647

[chrisbobbe]

(Should we add this to #309?)

[gnprice]

This is one of the pieces of:

• Convert message list to new, 2023+ design #157

in that the styling we have matches what was current in web when I started the prototype, but hasn't been updated.

Having this separate issue in the tracker is useful, though — for actually tackling #157, we'll probably want separate issues like this one anyway. And it provides an on-point answer for someone wondering why it doesn't match web. I'll edit #157 to point to this.

[gnprice]

We've already done the first part of this: the mentions no longer look like the first screenshot above. Instead they always look like the blue pill in the second screenshot.

The remaining task is to have the distinct styling for group mentions.