refactor: remove Douyin, Weibo and WeChat channels (#347)

All three had rotted past honest usability:
- Douyin's upstream (yzfly/douyin-mcp-server) is archived and required a
  4-step manual local-server setup nobody could complete
- Weibo depended on an unmaintained personal fork (mcp-server-weibo)
- WeChat full-article reading was increasingly blocked by anti-bot
  (#339) while doctor still advertised it as zero-config

Removes the channel files, installers, skill routing/trigger entries,
reference sections and README rows (zh+en). Honest counts: 13 platforms,
6 zero-config. They can return when maintained upstreams exist.

Follows the v1.4.0 precedent of removing Discord/Toutiao (#234).

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

agent_reach/guides/setup-wechat.md

@@ -1,40 +0,0 @@
-# 微信公众号配置指南
-
-## 功能说明
-读取微信公众号文章。需要 Playwright 来处理微信的反爬机制。
-
-## Agent 可自动完成的步骤
-
-1. 检查 Playwright 是否安装：
-```bash
-python3 -c "import playwright; print('installed')" 2>&1
-```
-
-2. 安装 Playwright + 浏览器：
-```bash
-pip install playwright
-playwright install chromium
-```
-
-3. 安装完成后测试：
-```bash
-curl -s "https://r.jina.ai/https://mp.weixin.qq.com/s/一个测试链接" -H "Accept: text/markdown"
-```
-
-## 需要用户手动做的步骤
-
-请告诉用户：
-
-> 微信公众号的配置很简单，只需要安装一个浏览器组件（约 150MB）。
->
-> 我来帮你安装，你不需要做任何事情。安装过程大约 1-2 分钟。
->
-> 安装好之后就可以直接读取微信公众号文章了，不需要登录。
-
-## Agent 操作流程
-
-1. 安装 Playwright：`pip install playwright`
-2. 安装 Chromium：`playwright install chromium`
-3. 测试：读一篇微信文章
-4. 反馈："✅ 微信公众号已配置！发给我任何公众号文章链接，我都能读取。"
-5. 如果安装失败（空间不足等）："❌ 浏览器组件安装失败。可能是磁盘空间不足（需要约 150MB）。"