feat(freeze): no authors in the config, no author check

A repository that takes commits from people it cannot list has no way
to freeze a range today: a null `authors` falls back to
`git config user.email`, so every foreign author or committer fails.
Null, or no key, now means neither is checked; the freeze warns that it
did not check them and records `authors` as null. A list is checked as
before. An empty list, which no commit could pass, is a config error
that points at null.
Released as 1.1.0.

process/prepush.md

@@ -136,7 +136,7 @@ delta `@{upstream}..HEAD`, the rule for a repository that pushes to its
 own trunk; `base`: always the merge-base with `base`, the whole pull request
 for a repository whose branches become PRs — their commits must be linear,
 rebased, never a merge of the integration branch), `authors` (the emails the
-freeze accepts; null = `git config user.email`), `aiTrailers` (`forbid` or
+freeze accepts; null = neither author nor committer is checked), `aiTrailers` (`forbid` or
 `allow`), `requireSigned`, `allowDirty` (tracked
 files the local stack rewrites in place while the lenses run), `gate0` (the
 commands Gate 0 runs by hand, for the skill), `modes` (`modes.<name>`: the
@@ -209,8 +209,9 @@ default), `notes`.
    output where a commit message's "tested" claim can point at it
    (`--context-paths`).
 2. **Freeze** — `freeze` checks, all of them, before it
-   exports anything: author AND committer are in `authors`; AI attribution
-   trailers (`Assisted-by:`, `Co-Authored-By:`) by the `aiTrailers` rule; the
+   exports anything: author AND committer are in `authors` (when it is
+   set); AI attribution trailers (`Assisted-by:`, `Co-Authored-By:`) by the
+   `aiTrailers` rule; the
    tracked tree is clean (the `allowDirty` paths aside, warned); no merge
    commit in the range (`git format-patch` drops them silently, so the
    artifact would not be the push); the range is a fast-forward of