feat(dev-workflow): Phase 1 - 技能框架搭建

- 创建 SKILL.md 定义9阶段流程
- 定义触发词: '开始开发...'
- 创建状态文件结构 state.json
- 创建需求收集模板 requirements.json
- 创建状态管理工具 state_manager.py
- 支持跨会话状态恢复

.planning/dev-workflow/requirements.json

@@ -0,0 +1,22 @@
+{
+  "schema": "dev-workflow-requirements-v1",
+  "collected_at": null,
+  "project_type": null,
+  "summary": {
+    "name": null,
+    "description": null,
+    "core_value": null
+  },
+  "functional_requirements": [],
+  "technical_requirements": {
+    "language": null,
+    "framework": null,
+    "database": null,
+    "dependencies": []
+  },
+  "constraints": [],
+  "acceptance_criteria": [],
+  "out_of_scope": [],
+  "questions_asked": [],
+  "user_answers": []
+}