fix(xiaohongshu): improve search login-wall handling and detail output

[xiaokuili]

Description

Improve xiaohongshu search in two ways:

1. Detect the Xiaohongshu search login wall and return an explicit error instead of silently returning [].
2. Enrich search results with note detail data so the command returns:
   • a directly usable detail URL from the search result page
   • note content
   • comment count
   • top comments

This also fixes URL handling.
Previously the command could degrade result URLs into bare /explore/<noteId> links, which were not reliably reopenable.
Now it preserves the real detail link exposed by the search result page (search_result/...?...xsec_token=...), so the returned url can open the note detail page directly.

Related issue: #296

Type of Change

• 🐛 Bug fix
• ✨ New feature
• 🌐 New site adapter
• 📝 Documentation
• ♻️ Refactor
• 🔧 CI / build / tooling

Checklist

• I ran the checks relevant to this PR
• I updated tests or docs if needed
• I included output or screenshots when useful

Documentation (if adding/modifying an adapter)

• Added doc page under docs/adapters/ (if new adapter)
• Updated docs/adapters/index.md table (if new adapter)
• Updated sidebar in docs/.vitepress/config.mts (if new adapter)

Screenshots / Output

Checks run:

npx tsc --noEmit
npx vitest run src/

Added tests:

• explicit login-wall error for xiaohongshu search
• preserving the search_result detail URL and enriching rows with note detail fields

Before

{
  "rank": 2,
  "title": "某鱼买FSD被坑了4万",
  "author": "随风2025-10-10",
  "likes": "261",
  "url": "https://www.xiaohongshu.com/explore/68e90be80000000004022e66",
  "author_url": "https://www.xiaohongshu.com/user/profile/635a9c720000000018028b40?...",
  "content": "",
  "comment_count": "0",
  "comments": []
}

After

{
  "rank": 2,
  "title": "某鱼买FSD被坑了4万",
  "author": "随风",
  "likes": "261",
  "url": "https://www.xiaohongshu.com/search_result/68e90be80000000004022e66?xsec_token=...",
  "author_url": "https://www.xiaohongshu.com/user/profile/635a9c720000000018028b40?...",
  "content": "今天早上提车，昨天深夜，心血来潮搜了一下x鱼...",
  "comment_count": "302",
  "comments": [
    "KA330: 没有被坑啊。",
    "NONO: 你怎么敢某鱼花4.3W买的"
  ]
}

The After URL is taken from the real search-result detail link and can open the note detail page directly.