a2ml: rename misnamed runbook out of the .launcher.a2ml namespace

This file uses the hand-written runbook schema ([metadata], [launcher],
[subcommands], [paths], …), not the launch-scaffolder launcher schema
([project], [repo], [runtime]). Sharing the `.launcher.a2ml` extension
caused `launch-scaffolder realign` to try to parse it as a launcher
config and fail with "missing field `project`".

Rename to `.runbook.a2ml` so the scaffolder no longer picks it up.
Content is preserved verbatim.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath