docs: add Claude Code co-author trailer rule

Document that commits created through Claude Code should include
`Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>`, mirroring
the existing Codex trailer convention in both README and SKILL.md.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: r1tsuu

.agents/skills/craftvale/SKILL.md

@@ -77,6 +77,8 @@ task touches a feature area with an existing implementation plan.
   commit should include a body describing what changed.
 - Commits created through Codex should include the trailer
   `Co-authored-by: Codex <codex@openai.com>`.
+- Commits created through Claude Code should include the trailer
+  `Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>`.
 - Prefer updating `plans/000N-*.md` when a feature meaningfully changes scope or
   architecture.
 

README.md

@@ -145,6 +145,7 @@ Content authoring and generation now live in [`architecture.md`](./architecture.
 - Keep the subject short and action-oriented, for example `feat: add player-name profiles`.
 - Every commit should include a body that explains what changed and why.
 - Commits created through Codex should include `Co-authored-by: Codex <codex@openai.com>`.
+- Commits created through Claude Code should include `Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>`.
 
 ## Editor Setup