Introduce `missing_required_trailers()` and `git.private-commits` scaffolding: `described()`, `wip()`, `has_trailer(pattern)`, and `missing_trailer(pattern)` revset aliases, defaulting to `none()` so they're inert everywhere until a repo's `settings.scopes` entry overrides them. Surface the advisory in the log template via `trailer_warning(commit)`, rendered as a red `[!missing trailer]` tag on mutable, non-empty commits. Wire it up for two repos: `~/sweetwater` requires a `Jira:` trailer, `~/work/some-repo` requires `Signed-off-by:`; both also mark `wip()` commits private so they never get flagged as push-ready.