add frontend-design rule, fix codex-reviewer, route table update

- add .claude/rules/frontend.md: auto-loads /frontend-design for ui/** files
- add frontend-design to CLAUDE.md route table
- fix codex reviewer: use direct Bash instead of subagent (permissions issue)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -39,6 +39,7 @@ This file provides guidance to Claude Code (claude.ai/code) when working with co
 | GCP commands | `/gcloud` skill |
 | Stress-test a decision | `/critic` skill |
 | Audit agent config quality | `/ax` skill |
+| Frontend/UI work | `/frontend-design` skill (auto-loaded for `ui/**` files) |
 
 ## Git (Gitea)