Auto-lock function + Large-area coloring optimization

1. Auto block locking function: Once all blocks with the same color ID in the image are fully drawn, they will be automatically locked. No other colors can be drawn on locked blocks to prevent accidental brush touches.

2. Large-area coloring optimization: Fast drawing no longer produces broken lines. A high-speed drawing fill-completion feature is added. The success rate of triggering automatic large-area filling at canvas edges has been raised to 100%.