feat: add WeChat Official Account channel (#54) (#67)

New channel: wechat (微信公众号文章)
- Backend: wechat-article-for-ai (Camoufox stealth browser)
- Can read mp.weixin.qq.com article URLs → clean Markdown
- Bypasses WeChat anti-bot detection via stealth Firefox
- Doctor checks for camoufox package availability
- SKILL.md updated with usage examples

Co-authored-by: Panniantong <panniantong@users.noreply.github.com>

agent_reach/channels/wechat.py

@@ -0,0 +1,32 @@
+# -*- coding: utf-8 -*-
+"""WeChat Official Account articles — check if wechat-article-for-ai is available."""
+
+import shutil
+import subprocess
+from .base import Channel
+
+
+class WeChatChannel(Channel):
+    name = "wechat"
+    description = "微信公众号文章"
+    backends = ["wechat-article-for-ai (Camoufox)"]
+    tier = 2
+
+    def can_handle(self, url: str) -> bool:
+        from urllib.parse import urlparse
+        d = urlparse(url).netloc.lower()
+        return "mp.weixin.qq.com" in d or "weixin.qq.com" in d
+
+    def check(self, config=None):
+        try:
+            import camoufox  # noqa: F401
+        except ImportError:
+            return "off", (
+                "需要 wechat-article-for-ai。安装：\n"
+                "  pip install camoufox[geoip] markdownify beautifulsoup4 httpx mcp\n"
+                "  # 或完整安装：\n"
+                "  git clone https://github.com/bzd6661/wechat-article-for-ai.git\n"
+                "  cd wechat-article-for-ai && pip install -r requirements.txt\n"
+                "  详见 https://github.com/bzd6661/wechat-article-for-ai"
+            )
+        return "ok", "可读取微信公众号文章（URL → Markdown）"