add help docs and ?

docs/nodes/Inverse 2D FFT.md

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+# Inverse 2D FFT
+
+Reconstruct a spatial-domain image from a 2D frequency spectrum. For exact reconstruction, connect magnitude/phase (or log magnitude/phase, or PSDF/phase) from the 2D FFT node. If phase is omitted, zero phase is assumed.
+
+## Inputs
+
+| Name | Type | Required | Description |
+|------|------|----------|-------------|
+| spectrum | DATA_FIELD | Yes | Frequency-domain field (output of FFT 2D) |
+| phase | DATA_FIELD | No | Phase field; if omitted, zero phase is used |
+
+## Outputs
+
+| Name | Type | Description |
+|------|------|-------------|
+| image | DATA_FIELD | Reconstructed spatial-domain field |
+
+## Controls
+
+| Name | Type | Default | Description |
+|------|------|---------|-------------|
+| representation | dropdown | magnitude | How to interpret the spectrum input: magnitude, log_magnitude, or psdf |
+
+## Limitations
+
+- The spectrum input must be a frequency-domain DATA_FIELD; connecting a spatial-domain field raises an error.
+- If phase is connected, it must also be a frequency-domain field with the same shape as the spectrum.
+- Reconstruction from PSDF (which discards phase) assumes zero phase and produces a symmetric result.