v16.0.0

fix: rebase onto local master instead of stale origin/master

The merge queue and coding agent prompt used `git fetch origin && git rebase
origin/master`, but the container has no SSH keys so fetch fails silently.
After the merge queue merges a ticket into local master, origin/master stays
stale. Subsequent ticket branches rebasing onto origin/master would rewind
past prior merges, causing persistent merge conflicts.

Remove the fetch and rebase onto local `master` directly.

Also bumps version to v16.0.0 (loop system complete).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>