docs(refactor[ext]): Document {toolicon} as alias for {tooliconl}

why: _toolicon_role and _tooliconl_role were identical with no comment,
looking like an incomplete refactoring step.
what:
- Add clarifying comment explaining the intentional alias

Author: tony

docs/_ext/fastmcp_autodoc.py

@@ -1036,6 +1036,7 @@ def role_fn(
     return role_fn
 
 
+# {toolicon} is a convenience alias for {tooliconl} (both render icon-left)
 _toolicon_role = _make_toolicon_role("left")
 _tooliconl_role = _make_toolicon_role("left")
 _tooliconr_role = _make_toolicon_role("right")