add help docs and ?

docs/nodes/ACF 1D.md

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+# ACF 1D
+
+Compute the one-dimensional autocorrelation function of a line profile. Only positive lags are output on the x-axis. The measurement table reports the dominant period from the first positive peak.
+
+## Inputs
+
+| Name | Type | Required | Description |
+|------|------|----------|-------------|
+| profile | LINE | Yes | Input line profile |
+
+## Outputs
+
+| Name | Type | Description |
+|------|------|-------------|
+| acf | LINE | Autocorrelation function (positive lags only) |
+| measurement | RECORD_TABLE | Table with the dominant peak period |
+
+## Controls
+
+| Name | Type | Default | Description |
+|------|------|---------|-------------|
+| level | dropdown | mean | Pre-processing: subtract mean before correlation, or none |
+
+## Limitations
+
+- Only one-sided (positive lag) ACF is returned.
+- Peak period detection finds only the first local maximum; multi-periodic signals report only the shortest detected period.