fix(web): keep mention suggestions accessible in writing forms #215

Mention suggestions can be positioned outside their text field or clipped by surrounding scrolling and animated containers. Inconsistent anchoring also makes completion behavior vary across writing forms.

Use a shared caret-anchored overlay that retains the existing card presentation and field focus, avoids viewport edges, and remains interactive inside modal writing surfaces. Keep keyboard selection, input composition, blur dismissal, and suggestion-first Escape handling consistent.

Implementation

#216