Naming things: `OutlineItems.to_dict()` is semantically wrong

## Problem

The method name `to_dict()` here is obviously wrong, because the method returns a `list` type.

```python
class OutlineItems(list):
    """List of `OutlineItem` elements, including additional features"""

    def to_dict(self):
        return [item.to_dict() for item in self]
```

## References
- https://github.com/crate/cratedb-mcp/pull/60#discussion_r2222398618