remove unused devflow/reference and ignore .codex

- devflow/reference/ was a placeholder from initial design with no write/read rules defined across v2-v4 iterations
- .codex/ is tool-generated and should not be tracked

.agents/skills/sm-flow/references/operating-rules.md

@@ -38,7 +38,6 @@
    - `devflow/projects/`
    - `devflow/glossary/CONTEXT.md`
    - `devflow/compound/`
-   - `devflow/reference/`
 4. 如果根目录存在旧 `CONTEXT.md`，且 `devflow/glossary/CONTEXT.md` 不存在或为空，询问用户是迁移还是合并。
 5. 检查 OpenSpec 和子 skill 是否可用：
    - OpenSpec 能力：`openspec-propose`、`openspec-apply-change`、`openspec-archive-change`。

.gitignore

@@ -1,4 +1,5 @@
 skill-workbench/validation/project/
 superpowers/
 .claude/
+.codex/
 *.stackdump