This PR makes it so we always show the "Add Context {keybinding}" text
when there's no context pills attached. Also, while we haven't fully
implemented the mention system (triggered by typing `@`), we removed the
instruction on the message editor placeholder. Once that's fully in
place, we should return with it!
<img width="800" alt="Screenshot 2024-12-27 at 1 35 56 PM"
src="https://github.com/user-attachments/assets/201cf784-e7ac-420a-adf2-51b6e075c2b6"
/>
Release Notes:
- N/A
---------
Co-authored-by: Agus Zubiaga <hi@aguz.me>