Small follow-up to the featured-effects explorer.
Added
- Drop an image straight onto the featured-effects preview — the preview is now a file drop target (with a ring + "Drop image to replace" overlay) for the image-based effects (Dithering, Halftone, Halftone dots, Fluted glass), not just the sidebar upload. Drag-to-pan and scroll/pinch-to-zoom are unchanged; generative effects without an image stay non-droppable. Docs-explorer only — no registry block changed.
Full diff: #12