adding more nodes

docs/nodes/Frequency Split.md

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+# Frequency Split
+
+Separate a DATA_FIELD into low-frequency and high-frequency components using an FFT-based Gaussian filter. The low-pass output contains smooth, large-scale variations while the high-pass output contains fine detail and noise. Equivalent to Gwyddion's `freq_split.c` module.
+
+## Inputs
+
+| Name | Type | Required | Description |
+|------|------|----------|-------------|
+| field | DATA_FIELD | Yes | Input field to split |
+
+## Outputs
+
+| Name | Type | Description |
+|------|------|-------------|
+| low_pass | DATA_FIELD | Low-frequency (smoothed) component |
+| high_pass | DATA_FIELD | High-frequency (detail) component |
+
+## Controls
+
+| Name | Type | Default | Description |
+|------|------|---------|-------------|
+| cutoff | FLOAT | 0.1 | Cutoff frequency as a fraction of Nyquist (0.001–0.5) |
+
+## Notes
+
+- The cutoff is relative to the Nyquist frequency. A value of 0.5 effectively passes everything (no filtering), while 0.001 aggressively removes nearly all spatial frequencies from the low-pass output.
+- The two outputs always sum to the original field: low_pass + high_pass = input.
+- Useful for separating roughness from waviness, or for removing long-range background while preserving features.
+- The filter operates in the frequency domain via FFT, so it handles periodic boundaries naturally.