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

agent_reach/integrations/mcp_server.py

@@ -5,7 +5,7 @@ Agent Reach MCP Server — expose doctor/status as MCP tool.
 Run: python -m agent_reach.integrations.mcp_server
 
 Agent Reach is an installer + doctor tool. For actual reading/searching,
-agents should call upstream tools directly (xreach, yt-dlp, mcporter, etc.).
+agents should call upstream tools directly (bird, yt-dlp, mcporter, etc.).
 """
 
 import asyncio