feat(twitter): migrate from xreach to bird CLI

- Replace xreach CLI with bird (@steipete/bird) as Twitter/X backend
- bird uses AUTH_TOKEN/CT0 env vars (simpler than xreach's session.json)
- Accept both 'bird' and 'birdx' binary names
- Remove version detection logic (bird v0.8.0 is the baseline)
- Write credentials.env to ~/.config/bird/ for easy sourcing
- Keep xfetch session.json sync for backward compatibility
- Update SKILL.md commands: bird search/read/user-tweets/thread
- Update install/uninstall to use npm @steipete/bird
- All 52 tests pass

docs/install.md

@@ -20,7 +20,7 @@ Copy this to your AI Agent:
 
 ### Goal
 
-Install Agent Reach and all upstream tools so your user's agent has full internet access. After installation, you'll use the upstream tools directly (xreach CLI, yt-dlp, mcporter, gh CLI, etc.) — Agent Reach is just the installer and health checker.
+Install Agent Reach and all upstream tools so your user's agent has full internet access. After installation, you'll use the upstream tools directly (bird CLI, yt-dlp, mcporter, gh CLI, etc.) — Agent Reach is just the installer and health checker.
 
 ### ⚠️ Boundaries
 
@@ -63,7 +63,7 @@ pip install https://github.com/Panniantong/agent-reach/archive/main.zip
 agent-reach install --env=auto
 ```
 
-This auto-installs system dependencies (gh CLI, Node.js, mcporter, xreach), configures Exa search, detects environment, and tests all channels.
+This auto-installs system dependencies (gh CLI, Node.js, mcporter, bird), configures Exa search, detects environment, and tests all channels.
 
 > 💡 **macOS / Homebrew Python 提示 `externally-managed-environment`？**
 > 这是 PEP 668 保护，不是 Agent Reach 本身的问题。优先用 `pipx install ...`，或先创建 `venv` 再安装。
@@ -129,13 +129,12 @@ agent-reach configure twitter-cookies "PASTED_STRING"
 
 > **代理说明（中国大陆等需要翻墙的网络环境）：**
 >
-> xreach CLI 使用 Node.js 原生 `fetch()`，默认不走系统代理（`HTTP_PROXY`/`HTTPS_PROXY`）。
-> Agent Reach 已内置解决方案：安装时会自动安装 `undici`（`npm install -g undici`），
-> 运行 xreach 时自动注入 `EnvHttpProxyAgent`，让 fetch 走用户配置的代理。
+> bird CLI 使用 Node.js，在需要代理的网络环境下可通过环境变量配置代理。
+> Agent Reach 安装时会自动安装 `undici`（`npm install -g undici`）以提供代理支持。
 >
 > **你（Agent）需要做的：**
-> 1. 确认 `undici` 已全局安装：`npm list -g undici`，没有就装：`npm install -g undici`
-> 2. 确认用户配了代理：`agent-reach configure proxy http://user:pass@ip:port`
+> 1. 确认用户配了代理：`agent-reach configure proxy http://user:pass@ip:port`
+> 2. 设置环境变量：`export HTTP_PROXY="..." HTTPS_PROXY="..."`
 > 3. Agent Reach 会自动处理剩下的，不需要用户做额外操作
 >
 > 如果用户报告 "fetch failed"，参考 [troubleshooting.md](troubleshooting.md)
@@ -325,7 +324,7 @@ After installation, use upstream tools directly. See SKILL.md for the full comma
 
 | Platform | Upstream Tool | Example |
 |----------|--------------|---------|
-| Twitter/X | `xreach` | `xreach search "query" --json` |
+| Twitter/X | `bird` | `bird search "query" -n 10` |
 | YouTube | `yt-dlp` | `yt-dlp --dump-json URL` |
 | Bilibili | `yt-dlp` | `yt-dlp --dump-json URL` |
 | Reddit | `curl` | `curl -s "https://reddit.com/r/xxx.json"` |