add help docs and ?

docs/nodes/Spot Removal.md

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+# Spot Removal
+
+Fill defect pixels (hot pixels, dropouts, scan artifacts) by interpolation. The mask defines defect locations. Equivalent to Gwyddion spotremove.c.
+
+## Inputs
+
+| Name | Type | Required | Description |
+|------|------|----------|-------------|
+| field | DATA_FIELD | Yes | Input field with defect pixels |
+| mask | IMAGE | No | Binary mask marking defect pixel locations; if omitted, no inpainting is performed |
+
+## Outputs
+
+| Name | Type | Description |
+|------|------|-------------|
+| result | DATA_FIELD | Field with defect pixels replaced by interpolated values |
+
+## Controls
+
+| Name | Type | Default | Description |
+|------|------|---------|-------------|
+| method | dropdown | laplace | Inpainting method: laplace (smooth Laplace equation solution), mean (local mean), or zero |
+| max_iter | INT | 100 | Maximum number of iterations for the Laplace solver (1–2000) |
+
+## Limitations
+
+- Large masked regions may not converge fully within max_iter iterations using the Laplace method.
+- The mean method uses a simple neighbourhood average and may leave visible discontinuities at large defect clusters.