plannotator-tui: hand a document to the human for review

Only when HERDR_ENV=1 (you are running inside Herdr). Otherwise tell the human where the file is and ask them to review it.

1. Write the document to a file. Do not paste it into chat as well.

2. Open it for review, from your own pane:

   plannotator-tui herdr open docs/plans/auth.md
   

   plannotator-tui opens beside you (or wherever the user configured it), already knowing that feedback comes back to this pane.

3. End your turn. Do not wait, poll, or read the pane. The review arrives as the next user message, as numbered feedback:

   # Annotations on docs/plans/auth.md