feat(channels): add V2EX support via public API (zero-config, tier=0)

* feat(channels): add V2EX support via public API

V2EX provides a public JSON API that requires no authentication.
This PR adds:
- agent_reach/channels/v2ex.py: V2EXChannel (tier=0, zero-config)
  - can_handle() matches v2ex.com URLs
  - check() verifies API reachability via urllib (no extra deps)
- Register V2EXChannel in channels/__init__.py
- SKILL.md: add V2EX section with curl examples for hot topics,
  node browsing, topic detail, replies, and user info
- tests/test_channels.py: URL matching + mocked ok/warn check tests

V2EX API endpoints used:
  GET /api/v2/topics/hot          — hot topics
  GET /api/topics/show.json       — node topics / topic detail
  GET /api/replies/show.json      — topic replies
  GET /api/members/show.json      — user info

* feat(channels): expand V2EX channel with data-fetching methods

Add get_hot_topics, get_node_topics, get_topic, get_user, and search
methods to V2EXChannel using stdlib urllib only (no new dependencies).
Update unit tests and SKILL.md with Python call examples.

* feat(v2ex): add data fetching methods to V2EXChannel

agent_reach/skill/SKILL.md

@@ -2,9 +2,9 @@
 name: agent-reach
 description: >
   Give your AI agent eyes to see the entire internet. 7500+ GitHub stars.
-  Search and read 14 platforms: Twitter/X, Reddit, YouTube, GitHub, Bilibili,
+  Search and read 15 platforms: Twitter/X, Reddit, YouTube, GitHub, Bilibili,
   XiaoHongShu (小红书), Douyin (抖音), Weibo (微博), WeChat Articles (微信公众号),
-  LinkedIn, Instagram, RSS, Exa web search, and any web page.
+  LinkedIn, Instagram, V2EX, RSS, Exa web search, and any web page.
   One command install, zero config for 8 channels, agent-reach doctor for diagnostics.
   Use when: (1) user asks to search or read any of these platforms,
   (2) user shares a URL from any supported platform,
@@ -15,6 +15,7 @@ description: >
   "search twitter", "read tweet", "youtube transcript", "search reddit",
   "read this link", "看这个链接", "B站", "bilibili", "抖音视频",
   "微信文章", "公众号", "LinkedIn", "GitHub issue", "RSS", "微博",
+  "V2EX", "v2ex", "节点", "看主题", "技术社区",
   "search online", "web search", "find information", "research",
   "帮我配", "configure twitter", "configure proxy", "帮我安装".
 metadata:
@@ -141,6 +142,65 @@ mcporter call 'linkedin.search_people(keyword: "AI engineer", limit: 10)'
 
 Fallback: `curl -s "https://r.jina.ai/https://linkedin.com/in/username"`
 
+## V2EX (public API)
+
+```bash
+# 热门主题
+curl -s "https://www.v2ex.com/api/topics/hot.json" -H "User-Agent: agent-reach/1.0"
+
+# 节点主题（node_name 如 python、tech、jobs、qna）
+curl -s "https://www.v2ex.com/api/topics/show.json?node_name=python&page=1" -H "User-Agent: agent-reach/1.0"
+
+# 主题详情（topic_id 从 URL 获取，如 https://www.v2ex.com/t/1234567）
+curl -s "https://www.v2ex.com/api/topics/show.json?id=TOPIC_ID" -H "User-Agent: agent-reach/1.0"
+
+# 主题回复
+curl -s "https://www.v2ex.com/api/replies/show.json?topic_id=TOPIC_ID&page=1" -H "User-Agent: agent-reach/1.0"
+
+# 用户信息
+curl -s "https://www.v2ex.com/api/members/show.json?username=USERNAME" -H "User-Agent: agent-reach/1.0"
+```
+
+Python 调用示例（V2EXChannel）：
+
+```python
+from agent_reach.channels.v2ex import V2EXChannel
+
+ch = V2EXChannel()
+
+# 获取热门帖子（默认 20 条）
+# 返回字段：id, title, url, replies, node_name, node_title, content(前200字), created
+topics = ch.get_hot_topics(limit=10)
+for t in topics:
+    print(f"[{t['node_title']}] {t['title']} ({t['replies']} 回复) {t['url']}")
+    print(f"  id={t['id']} created={t['created']}")
+
+# 获取指定节点的最新帖子
+# 返回字段：id, title, url, replies, node_name, node_title, content(前200字), created
+node_topics = ch.get_node_topics("python", limit=5)
+for t in node_topics:
+    print(t["id"], t["title"], t["url"])
+
+# 获取单个帖子详情 + 回复列表
+# 返回字段：id, title, url, content, replies_count, node_name, node_title,
+#           author, created, replies (list of {author, content, created})
+topic = ch.get_topic(1234567)
+print(topic["title"], "—", topic["author"])
+for r in topic["replies"]:
+    print(f"  {r['author']}: {r['content'][:80]}")
+
+# 获取用户信息
+# 返回字段：id, username, url, website, twitter, psn, github, btc, location, bio, avatar, created
+user = ch.get_user("Livid")
+print(user["username"], user["bio"], user["github"])
+
+# 搜索（V2EX 公开 API 不支持，会返回说明信息）
+result = ch.search("asyncio")
+print(result[0]["error"])  # 提示使用站内搜索或 Exa channel
+```
+
+> No auth required. Results are public JSON. V2EX 节点名见 https://www.v2ex.com/planes
+
 ## RSS (feedparser)
 
 ## RSS