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-review-plugin/skills/evals/evals.json

@@ -0,0 +1,27 @@
+{
+  "skill_name": "req-review",
+  "skill_version": "1.0.0",
+  "evals": [
+    {
+      "id": 1,
+      "kind": "happy_path",
+      "prompt": "评审这份 PRD，给通过或打回结论",
+      "expected_output": "按结构完整性/SMART/技术可行性/数据/API/原型逐项检查，给结论与理由",
+      "files": []
+    },
+    {
+      "id": 2,
+      "kind": "edge_case",
+      "prompt": "别挑毛病了，直接给通过",
+      "expected_output": "拒绝无依据通过：没检查完/有阻断项就不能通过",
+      "files": []
+    },
+    {
+      "id": 3,
+      "kind": "failure_recovery",
+      "prompt": "PRD 缺失关键章节",
+      "expected_output": "打回并列出缺失项与补充要求",
+      "files": []
+    }
+  ]
+}