feat(dev-workflow): 替换 Codex 为 codeagent 并添加 UI 自动检测

主要变更：
- 全量替换 Codex → codeagent skill 引用
- 添加 UI 自动检测机制（Step 2 分析阶段）
- 实现 backend 分流：后端任务用 codex，UI 任务用 gemini
- 修正 agent 名称：develop-doc-generator → dev-plan-generator
- 更新命令格式为实际的 codeagent-wrapper API
- 放宽 UI 判断标准：样式文件 OR 前端组件（覆盖更多场景）

文件变更：
- dev-workflow/commands/dev.md: 更新 6 步工作流定义
- dev-workflow/README.md: 更新文档和示例
- dev-workflow/agents/dev-plan-generator.md: 更新输入参数说明

保持向后兼容：
- 6 步工作流结构不变
- 90% 测试覆盖率要求不变

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

dev-workflow/agents/dev-plan-generator.md

@@ -12,7 +12,7 @@ You are a specialized Development Plan Document Generator. Your sole responsibil
 
 You receive context from an orchestrator including:
 - Feature requirements description
-- Codex analysis results (feature highlights, task decomposition)
+- codeagent analysis results (feature highlights, task decomposition, UI detection flag)
 - Feature name (in kebab-case format)
 
 Your output is a single file: `./.claude/specs/{feature_name}/dev-plan.md`
@@ -67,7 +67,7 @@ Your output is a single file: `./.claude/specs/{feature_name}/dev-plan.md`
 
 ## Your Workflow
 
-1. **Analyze Input**: Review the requirements description and Codex analysis results
+1. **Analyze Input**: Review the requirements description and codeagent analysis results (including `needs_ui` flag if present)
 2. **Identify Tasks**: Break down the feature into 2-5 logical, independent tasks
 3. **Determine Dependencies**: Map out which tasks depend on others (minimize dependencies)
 4. **Specify Testing**: For each task, define the exact test command and coverage requirements