docs(skill): 覆盖率阶段 1 完成 —— core + req 全部补齐 evals 与四段式文档

- 新增 14 个技能的 evals/evals.json（每技能 3 条：正常/边界/失败恢复）
- 新增 14 篇 docs/skills/*.md（What/When/Common questions/It's working if）
- 覆盖 core：pm-ask、pm-risk（ai-proj 已于样板提交）
- 覆盖 req：req-audit/compare/design/dev/lookback/prd/prototype/research/retro/review/test-gate/workflow
- coverage: 38 -> 24（剩余 dev 类等进入阶段 2/3）

skills-req/req-workflow-plugin/skills/evals/evals.json

@@ -0,0 +1,27 @@
+{
+  "skill_name": "req-workflow",
+  "skill_version": "1.0.0",
+  "evals": [
+    {
+      "id": 1,
+      "kind": "happy_path",
+      "prompt": "讲一下需求从提出到归档的完整流程",
+      "expected_output": "按阶段化流程说明每阶段动作、门禁与交付物，明确交付终点是 released + PDV",
+      "files": []
+    },
+    {
+      "id": 2,
+      "kind": "edge_case",
+      "prompt": "能跳过 staging 直接上生产吗",
+      "expected_output": "不能：说明强制 staging 验收与原因",
+      "files": []
+    },
+    {
+      "id": 3,
+      "kind": "failure_recovery",
+      "prompt": "文档说已 released，但任务还没完成",
+      "expected_output": "指出状态不一致，按真实数据核对后再判断",
+      "files": []
+    }
+  ]
+}