refactor: move bundled skills tree to repo root skills/

- Relocate runtime/skills -> skills/; runtime_skills_root() prefers oclaw/skills
  with fallback to legacy runtime/skills for unmigrated trees.
- session-bootstrap hook handler resolves repo root via PROJECT_ROOT.
- Update architecture/migration docs and in-tree skill references.

Co-authored-by: Cursor <cursoragent@cursor.com>

skills/_workspace/generalist/multi-search-engine/config.json

@@ -0,0 +1,85 @@
+{
+  "name": "multi-search-engine",
+  "engines": [
+    {
+      "name": "Baidu",
+      "url": "https://www.baidu.com/s?wd={keyword}",
+      "region": "cn"
+    },
+    {
+      "name": "Bing CN",
+      "url": "https://cn.bing.com/search?q={keyword}&ensearch=0",
+      "region": "cn"
+    },
+    {
+      "name": "Bing INT",
+      "url": "https://cn.bing.com/search?q={keyword}&ensearch=1",
+      "region": "cn"
+    },
+    {
+      "name": "360",
+      "url": "https://www.so.com/s?q={keyword}",
+      "region": "cn"
+    },
+    {
+      "name": "Sogou",
+      "url": "https://sogou.com/web?query={keyword}",
+      "region": "cn"
+    },
+    {
+      "name": "WeChat",
+      "url": "https://wx.sogou.com/weixin?type=2&query={keyword}",
+      "region": "cn"
+    },
+    {
+      "name": "Shenma",
+      "url": "https://m.sm.cn/s?q={keyword}",
+      "region": "cn"
+    },
+    {
+      "name": "Google",
+      "url": "https://www.google.com/search?q={keyword}",
+      "region": "global"
+    },
+    {
+      "name": "Google HK",
+      "url": "https://www.google.com.hk/search?q={keyword}",
+      "region": "global"
+    },
+    {
+      "name": "DuckDuckGo",
+      "url": "https://duckduckgo.com/html/?q={keyword}",
+      "region": "global"
+    },
+    {
+      "name": "Yahoo",
+      "url": "https://search.yahoo.com/search?p={keyword}",
+      "region": "global"
+    },
+    {
+      "name": "Startpage",
+      "url": "https://www.startpage.com/sp/search?query={keyword}",
+      "region": "global"
+    },
+    {
+      "name": "Brave",
+      "url": "https://search.brave.com/search?q={keyword}",
+      "region": "global"
+    },
+    {
+      "name": "Ecosia",
+      "url": "https://www.ecosia.org/search?q={keyword}",
+      "region": "global"
+    },
+    {
+      "name": "Qwant",
+      "url": "https://www.qwant.com/?q={keyword}",
+      "region": "global"
+    },
+    {
+      "name": "WolframAlpha",
+      "url": "https://www.wolframalpha.com/input?i={keyword}",
+      "region": "global"
+    }
+  ]
+}