Replace per-pixel Python loop with vectorized torch.arange + slice
operations. Fix DifferentialDiffusion node position to avoid visual
overlap with SplitImageToTileList node 14 on the canvas.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Replicate SplitImageToTileList's get_grid_coords logic to find real
overlap regions between adjacent tiles. Fixes three bugs:
1. Bands were at overlap start instead of center (off by overlap/2)
2. Spurious bands generated beyond the actual tile grid
3. Edge tile seams placed at wrong position (ignoring boundary shift)
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
