Address research suggestion card review

The source link's name includes its visible text, the editor avatars carry
an "is editing" tooltip apart from the attribution with a separate live
region, Command Enter on an empty brief explains itself, the card uses the
shared research width, and the brief editor grows from its content where
field-sizing is unsupported.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>