Permit basic formatting in tab notes or window names

E.g., inline-only markdown, with `img` but no `a`. I think https://github.com/Holixus/nano-markdown can be tweaked to do this.

**Edit** maybe also https://github.com/omnidan/node-emoji ;)

Start by reviewing how TabFern displays tab notes and window names, then evaluate the referenced nano-markdown library and the possible node-emoji integration. Done means those names support basic inline formatting, including img but excluding a, with the intended formatting behavior agreed and demonstrated.

Written by the indexing model from the issue text.