feat(bird): add detection functions for Bird CLI

- is_bird_installed() checks if bird command is in PATH
- is_bird_authenticated() runs bird whoami to verify auth
- check_npm_available() checks if npm can install bird

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

scripts/lib/bird_x.py

@@ -0,0 +1,56 @@
+"""Bird CLI client for X (Twitter) search."""
+
+import json
+import shutil
+import subprocess
+import sys
+from datetime import datetime
+from typing import Any, Dict, List, Optional, Tuple
+
+
+def _log(msg: str):
+    """Log to stderr."""
+    sys.stderr.write(f"[Bird] {msg}\n")
+    sys.stderr.flush()
+
+
+def is_bird_installed() -> bool:
+    """Check if Bird CLI is installed.
+
+    Returns:
+        True if 'bird' command is available in PATH, False otherwise.
+    """
+    return shutil.which("bird") is not None
+
+
+def is_bird_authenticated() -> Optional[str]:
+    """Check if Bird is authenticated by running 'bird whoami'.
+
+    Returns:
+        Username if authenticated, None otherwise.
+    """
+    if not is_bird_installed():
+        return None
+
+    try:
+        result = subprocess.run(
+            ["bird", "whoami"],
+            capture_output=True,
+            text=True,
+            timeout=10,
+        )
+        if result.returncode == 0 and result.stdout.strip():
+            # Output is typically the username
+            return result.stdout.strip().split('\n')[0]
+        return None
+    except (subprocess.TimeoutExpired, FileNotFoundError, subprocess.SubprocessError):
+        return None
+
+
+def check_npm_available() -> bool:
+    """Check if npm is available for installation.
+
+    Returns:
+        True if 'npm' command is available in PATH, False otherwise.
+    """
+    return shutil.which("npm") is not None