add help docs and ?

docs/nodes/Color Map.md

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+# Color Map
+
+Build a reusable colormap. Choose a preset from the built-in palette list, or create a custom gradient with min/max colours and any number of intermediate stops.
+
+## Inputs
+
+None.
+
+## Outputs
+
+| Name | Type | Description |
+|------|------|-------------|
+| colormap | COLORMAP | Colormap specification for use with other nodes |
+
+## Controls
+
+| Name | Type | Default | Description |
+|------|------|---------|-------------|
+| mode | dropdown | preset | Switch between preset and custom gradient modes |
+| preset | dropdown | viridis | Built-in colormap preset name; visible when mode is preset |
+| stops | STRING (colormap editor) | default gradient | JSON array of color stops for the custom gradient; visible when mode is custom |
+
+## Limitations
+
+- Custom colormaps must include at least a minimum and maximum color stop.
+- Stops must be valid JSON; invalid JSON will raise an error.