Bring the architecture doc up to date with main (#131)

Record what is in use now: planning through lane D, start and resume,
publishing, merging the task's own pull request, and closing pull requests
on cancel. Update the module table, flows 3 and 4, stored data, the
roadmap and the known limits, including the missing issue-author guard (#108).

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

Author: mchwang