add help docs and ?

docs/nodes/Flip.md

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+# Flip
+
+Reflect a DATA_FIELD across the X axis (top/bottom) or Y axis (left/right). Physical extents are preserved, and stored markup overlays are mirrored with the data.
+
+## Inputs
+
+| Name | Type | Required | Description |
+|------|------|----------|-------------|
+| field | DATA_FIELD | Yes | Input field to flip |
+
+## Outputs
+
+| Name | Type | Description |
+|------|------|-------------|
+| field | DATA_FIELD | Flipped field |
+
+## Controls
+
+| Name | Type | Default | Description |
+|------|------|---------|-------------|
+| axis | dropdown | x | Flip axis: x flips top/bottom (vertical mirror), y flips left/right (horizontal mirror) |
+
+## Limitations
+
+- None.