Commits of agents carry a co-author trailer naming the model

A git wrapper (docker/git-coauthor -> /usr/local/lib/codecraft/bin/git) adds
--trailer "$CODECRAFT_COMMIT_TRAILER" right after the commit subcommand; the
agent shell puts it first on PATH and sets the trailer in the script itself
(works inside the sandbox, which clears the environment). Default text:
"Co-Authored-By: {model} ({provider}) via CodeCraft" (server.commit_trailer,
Settings -> General; empty = off). Git skips duplicates (amend, model wrote it).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CHANGELOG.md

@@ -3,6 +3,15 @@
 All notable changes to CodeCraft. Versions follow [Semantic Versioning](https://semver.org/);
 until 1.0, minor versions may contain breaking changes.
 
+## [Unreleased]
+
+### Added
+
+- **Commits of agents name the model:** every `git commit` an agent makes gets the trailer
+  `Co-Authored-By: <model> (<provider>) via CodeCraft` (a git wrapper in the agent shell, also in
+  the sandbox; your own commits stay unchanged). The text is set under *Settings → General*
+  (`server.commit_trailer`, `{model}`, `{provider}`, `{model_id}`; empty = off).
+
 ## [v202611-00020] – 2026-11-11
 
 ### Added