- Implemented a new crate `hcie-watercolor-brushes` containing watercolor brush presets and a procedural splat preview renderer.
- Integrated watercolor brushes into the iced GUI's Brushes panel, adding a new category for watercolor brushes.
- Updated the `BrushCategory` enum to include `Watercolor` and modified the rendering logic to display watercolor presets.
- Added functionality to generate watercolor splat thumbnails using a noise-based algorithm.
- Ensured that existing brush styles and engine crates remain unmodified, adhering to project constraints.
