Add Color Matching node; Laplacian Sharpen & Unsharp Masking effects
- New ColorMatchingNode: two image inputs, one output, LAB/RGB/Histogram
methods (LAB default). Live in-node preview recomputes in JS on method
switch, mirroring the Layer Blending preview pattern.
- Filter Ops: add "Laplacian Sharpen" (4-/8-neighbor kernel) and
"Unsharp Masking" (Gaussian amount/radius/threshold) effects, with
matching JS live-preview implementations, widget visibility, tooltips.
- Update README (now four nodes) and node registration.