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

tests/test_twitter_channel.py

@@ -2,7 +2,7 @@
 
 from unittest.mock import patch, Mock
 
-from agent_reach.channels.twitter import _detect_xreach_version, TwitterChannel
+from agent_reach.channels.twitter import TwitterChannel
 
 
 def _cp(stdout="", stderr="", returncode=0):
@@ -13,27 +13,58 @@ def _cp(stdout="", stderr="", returncode=0):
     return m
 
 
-def test_detect_xreach_version_prefers_npm_when_cli_version_is_stale():
-    with patch("shutil.which", return_value="/opt/homebrew/bin/npm"), patch(
-        "subprocess.run",
-        side_effect=[
-            _cp(stdout="0.3.0\n"),
-            _cp(stdout='{"dependencies":{"xreach-cli":{"version":"0.3.2"}}}'),
-        ],
-    ):
-        assert _detect_xreach_version("/opt/homebrew/bin/xreach") == "0.3.2"
-
-
-def test_twitter_channel_does_not_false_warn_when_npm_has_newer_xreach():
+def test_check_bird_found_and_auth_ok():
+    """bird found + bird check returns 0 → ok."""
     channel = TwitterChannel()
-    with patch("shutil.which", side_effect=lambda name: "/opt/homebrew/bin/xreach" if name == "xreach" else "/opt/homebrew/bin/npm"), patch(
+    with patch("shutil.which", side_effect=lambda name: "/usr/local/bin/bird" if name == "bird" else None), patch(
         "subprocess.run",
-        side_effect=[
-            _cp(stdout="0.3.0\n"),
-            _cp(stdout='{"dependencies":{"xreach-cli":{"version":"0.3.2"}}}'),
-            _cp(stdout="authenticated\n", returncode=0),
-        ],
+        return_value=_cp(stdout="Authenticated as @user\n", returncode=0),
     ):
         status, message = channel.check()
     assert status == "ok"
     assert "完整可用" in message
+
+
+def test_check_bird_found_auth_missing():
+    """bird found + bird check returns 1 with 'Missing credentials' → warn about auth."""
+    channel = TwitterChannel()
+    with patch("shutil.which", side_effect=lambda name: "/usr/local/bin/bird" if name == "bird" else None), patch(
+        "subprocess.run",
+        return_value=_cp(stderr="Missing credentials: AUTH_TOKEN and CT0 required\n", returncode=1),
+    ):
+        status, message = channel.check()
+    assert status == "warn"
+    assert "未配置认证" in message
+
+
+def test_check_bird_not_found():
+    """bird not found → warn with install hint for @steipete/bird."""
+    channel = TwitterChannel()
+    with patch("shutil.which", return_value=None):
+        status, message = channel.check()
+    assert status == "warn"
+    assert "@steipete/bird" in message
+
+
+def test_check_birdx_binary_accepted():
+    """birdx symlink is accepted as an alternative binary name."""
+    channel = TwitterChannel()
+    with patch("shutil.which", side_effect=lambda name: "/usr/local/bin/birdx" if name == "birdx" else None), patch(
+        "subprocess.run",
+        return_value=_cp(stdout="Authenticated as @user\n", returncode=0),
+    ):
+        status, message = channel.check()
+    assert status == "ok"
+    assert "完整可用" in message
+
+
+def test_check_bird_auth_failure_generic():
+    """bird check returns 1 without 'Missing credentials' → generic auth failure warn."""
+    channel = TwitterChannel()
+    with patch("shutil.which", side_effect=lambda name: "/usr/local/bin/bird" if name == "bird" else None), patch(
+        "subprocess.run",
+        return_value=_cp(stderr="Error: token expired\n", returncode=1),
+    ):
+        status, message = channel.check()
+    assert status == "warn"
+    assert "认证检查失败" in message