Streamline the main canvas component, type definitions, and paint
shader runtime. Removes unused code paths and redundant logic across
src/ and example/, resulting in a net reduction of ~460 lines.
Co-authored-by: Cursor <cursoragent@cursor.com>
Enables optional wall-1/wall-2… sub-regions with independent paint and undo, plus example toggle and unit tests.
Co-authored-by: Cursor <cursoragent@cursor.com>