Context completion should trigger in the context window

[tomgeorge]

The context window is not currently modifiable and should be where context completion triggers.

[tomgeorge]

@W3ND31 Do we wnat this to work how eca-emacs does where you add a context item right in the context window? It looks like the implementation exposes an add_context function in sidebar.lua that only adds the repo map, which suggests to me that you would type a context in the chat window and then call update_context?

[ericdallo]

I'm ok with completion with @ too in the chat and adding to context.
It's a better UX maybe that I thought only after implementing in emacs

[joaopluigi]

This was done in #52