docs(skill): 覆盖率阶段 2 完成 —— 全量 evals 与四段式文档清零

- 24 个技能补齐 evals（正常/边界/失败恢复）与 docs/skills/*.md
- 覆盖 dev 类、发布 runbook、karpathy 守则、PR/清单等
- coverage: 24 -> 0（40 个 promoted+model-invoked 全覆盖）

skills-dev/agent-browser-plugin/skills/evals/evals.json

@@ -0,0 +1,27 @@
+{
+  "skill_name": "agent-browser",
+  "skill_version": "1.0.0",
+  "evals": [
+    {
+      "id": 1,
+      "kind": "happy_path",
+      "prompt": "打开本地页面，点登录按钮并截图",
+      "expected_output": "先 snapshot 拿 ref 再 click，操作后 observe/截图确认，不硬编码选择器",
+      "files": []
+    },
+    {
+      "id": 2,
+      "kind": "edge_case",
+      "prompt": "直接用 CSS 选择器点登录按钮，别做 snapshot",
+      "expected_output": "优先 snapshot-ref 定位；选择器只作兜底并说明原因",
+      "files": []
+    },
+    {
+      "id": 3,
+      "kind": "failure_recovery",
+      "prompt": "页面加载超时或元素找不到",
+      "expected_output": "重新 snapshot 并报告页面状态，不做盲点；给出超时/选择器排查",
+      "files": []
+    }
+  ]
+}