Open the document research composer from Chat /research

Choosing Research in Chat, or sending a /research brief, now switches to
the document and opens the existing research composer after the last
paragraph with the brief filled in. The editor exposes this through a
host-owned ResearchLauncher that attaches the same ResearchDraftStore
path the / menu uses. Chat reuses the / menu's exported surface and row
classes. The notice remains only where research is unavailable.

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