add help docs and ?

docs/nodes/Mask Morphology.md

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+# Mask Morphology
+
+Apply morphological operations to a binary mask. Dilate expands regions, erode shrinks them, open (erode then dilate) removes small islands, and close (dilate then erode) fills small holes. Equivalent to Gwyddion's mask_morph.c.
+
+## Inputs
+
+| Name | Type | Required | Description |
+|------|------|----------|-------------|
+| mask | IMAGE | Yes | Binary mask to process |
+| field | DATA_FIELD | No | Optional field for preview background display |
+
+## Outputs
+
+| Name | Type | Description |
+|------|------|-------------|
+| mask | IMAGE | Morphologically processed binary mask |
+
+## Controls
+
+| Name | Type | Default | Description |
+|------|------|---------|-------------|
+| operation | dropdown | dilate | Morphological operation: dilate, erode, open, or close |
+| radius | INT | 1 | Structuring element radius in pixels (1–50) |
+| shape | dropdown | disk | Structuring element shape: disk or square |
+
+## Limitations
+
+- Large radius values (> ~20 pixels) may be slow on large masks.