General Brush Engine Improvements

Features 1. Per-brush opt-in for scene-level brush settings (“use unified xxx”). 2. Brush tip roundness (currently available in limited brushes). 3. Customizable pressure curves for all pressure-sensitive parameters. 4. Customizable brush toggling and improved toggle display. 5. Improved first-stroke responsiveness across relevant brushes. 6. Pressure handling improvements in anchored mode. Deliverables 1. Tip roundness and tilt support across all relevant brushes. 2. Per-brush “use unified xxx” support. 3. Custom curve controls for all pressure-sensitive parameters, including auto-smooth and hardness. 4. Improved brush toggle UI and behavior. 5. Improved first-stroke responsiveness for relevant brushes. 6. Improved anchored-mode pressure handling. 7. End-user documentation for new features.