add help docs and ?

docs/nodes/Tip Deconvolution.md

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+# Tip Deconvolution
+
+Reconstruct the true surface from a tip-broadened measured AFM image. Uses morphological grey erosion (Villarrubia algorithm). Equivalent to gwy_tip_erosion (tip.c).
+
+## Inputs
+
+| Name | Type | Required | Description |
+|------|------|----------|-------------|
+| field | DATA_FIELD | Yes | Measured AFM image |
+| tip | DATA_FIELD | Yes | Tip shape field, e.g. from Tip Model or Blind Tip Estimate |
+
+## Outputs
+
+| Name | Type | Description |
+|------|------|-------------|
+| surface | DATA_FIELD | Reconstructed true surface |
+
+## Controls
+
+None.
+
+## Limitations
+
+- The tip pixel size must match the image pixel size exactly; mismatched calibrations will produce incorrect results.
+- Deconvolution can only reduce tip broadening; it cannot recover information lost below the noise floor.
+- Very large tip sizes are slow due to the nested loop over all tip pixels.