Add way to easily share GIFs

- [ ] write code that returns list of gifs for search term
- [ ] add layout option that works both on mobile and desktop, options:
- add "share gif" in attachment menu which opens a (which docks on the bottom part of the screen on mobile)
- add composer completion and floating picker
- show it in the right panel (nah?)

The issue names no files, tests, or entry points. Start by clarifying the GIF search source and which interface is in scope: attachment menu, composer completion, floating picker, or right panel. Done is not defined because the proposed layout and feature set remain undecided.

Written by the indexing model from the issue text.