feat: add Xueqiu (雪球) channel (#198)

* feat: add Xueqiu (雪球) channel for stock quotes and community posts

Add a Tier 0 (zero-config) channel for Xueqiu, China's popular stock
market and investment community platform. Uses auto-generated session
cookies via http.cookiejar — no login required.

Supported methods:
- get_stock_quote(symbol) — real-time quotes (A/HK/US markets)
- search_stock(query) — search by name or code
- get_hot_posts(limit) — trending community posts
- get_hot_stocks(limit, stock_type) — popular stocks leaderboard

Inspired by https://github.com/jackwener/opencli xueqiu implementation.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: add Xueqiu to README platform tables, remove stale Instagram ref

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: fernando_jacob <f.jacob1996@gmail.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

README.md

@@ -80,6 +80,7 @@ AI Agent 已经能帮你写代码、改文档、管项目——但你让它去
 | 💬 **微信公众号** | 搜索 + 阅读公众号文章（全文 Markdown） | — | 无需配置 |
 | 📰 **微博** | 热搜、搜索内容/用户/话题、用户动态、评论 | — | 无需配置 |
 | 💻 **V2EX** | 热门帖子、节点帖子、帖子详情+回复、用户信息 | — | 无需配置 |
+| 📈 **雪球** | 股票行情、搜索股票、热门帖子、热门股票排行 | — | 无需配置 |
 | 🎙️ **小宇宙播客** | — | 播客音频转文字（Whisper 转录，免费 Key） | 告诉 Agent「帮我配小宇宙播客」 |
 
 > **不知道怎么配？不用查文档。** 直接告诉 Agent「帮我配 XXX」，它知道需要什么、会一步一步引导你。