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

agent_reach/cli.py

@@ -283,7 +283,26 @@ def _install_system_deps():
         except Exception:
             print("  ⚠️  Node.js install failed. Install manually: https://nodejs.org")
 
+    # ── birdx (for Twitter search) ──
+    if shutil.which("birdx"):
+        print("  ✅ birdx already installed")
+    else:
+        if shutil.which("pip3") or shutil.which("pip"):
+            pip_cmd = "pip3" if shutil.which("pip3") else "pip"
+            try:
+                subprocess.run(
+                    [pip_cmd, "install", "-q", "birdx"],
+                    capture_output=True, text=True, timeout=120,
+                )
+                if shutil.which("birdx"):
+                    print("  ✅ birdx installed (Twitter search + timeline)")
+                else:
+                    print("  ⬜ birdx install failed (optional — Twitter reading still works via Jina)")
+            except Exception:
+                print("  ⬜ birdx install failed (optional — Twitter reading still works via Jina)")
 
+
+def _install_mcporter():
     """Install mcporter and configure Exa + XiaoHongShu MCP servers."""
     import shutil
     import subprocess