fix: 修复 _install_mcporter 函数丢失 + browser-cookie3 硬依赖 + 自动装 birdx

关键修复：
1. _install_mcporter() 函数定义被上次编辑误删（NameError 崩溃）
   → 恢复为独立函数
2. browser-cookie3 作为硬依赖在服务器上安装失败（缺 dbus/secretstorage）
   → 改为 optional[cookies]
3. birdx 不在自动安装流程中
   → _install_system_deps 增加自动 pip install birdx

install 流程现在完整覆盖：
  gh CLI → Node.js → birdx → mcporter → Exa → XHS → cookies → test

pyproject.toml

@@ -27,13 +27,11 @@ dependencies = [
     "pyyaml>=6.0",
     "rich>=13.0",
     "yt-dlp>=2024.0",
-    "browser-cookie3>=0.19",
 ]
 
 [project.optional-dependencies]
 browser = ["playwright>=1.40"]
 cookies = ["browser-cookie3>=0.19"]
-mcp = ["mcp[cli]>=1.0"]
 all = ["playwright>=1.40", "mcp[cli]>=1.0", "browser-cookie3>=0.19"]
 
 [project.scripts]