feat(logging): add token truncation helper

src/grist_mcp/logging.py

@@ -0,0 +1,11 @@
+"""Logging configuration and utilities."""
+
+
+def truncate_token(token: str) -> str:
+    """Truncate token to show first 3 and last 3 chars.
+
+    Tokens 8 chars or shorter show *** for security.
+    """
+    if len(token) <= 8:
+        return "***"
+    return f"{token[:3]}...{token[-3:]}"