This ensures the thread summary is treated as a tracked mention with
accessible context.
Changes:
- Fixed `MessageEditor::insert_thread_summary()` to use proper mention
URI format
- Added test coverage to verify the fix
Release Notes:
- Fixed an issue where "New From Summary" was not properly inserting
thread summaries as contextual mentions when creating new threads.
Thread summaries are now inserted as proper mention URIs.
743180342a