- Replace TCGA-HC-A8D1 with TCGA-HC-8265 as pre-bundled slide
- Remove pre-computed mask; segmentation now runs on-the-fly for all slides
- Cache tissue mask per slide path to avoid recomputation on param changes
- Pad mask overlay to match tiling preview dimensions (tile boundary alignment)
- Add PIL import at top level
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>