smargon: write chi/phi goniometer position into NXmx transformations

Add an optional Smargon static positioner (chi/phi angles + rotation axes)
that is reconstructed into the NXmx sample transformation chain. Chi/phi are
appended at the innermost end of the chain (closest to the sample) for both
the goniometer and grid-scan branches, with axes defaulting to chi {0,0,1}
and phi = omega default {1,0,0}.

- SmargonPosition gains chi_axis/phi_axis (common/JFJochMessages.h)
- OpenAPI: optional phi_axis/chi_axis arrays; clients regenerated
- OpenAPIConvert wires Dataset_settings.smargon -> DatasetSettings
- CBOR serializer/deserializer round-trip the axes
- tests: CBORSerialize_Start_Smargon

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/python_client/docs/DatasetSettings.md

@@ -39,6 +39,7 @@ Name | Type | Description | Notes
 **poni_rot3_rad** | **float** | PONI angle rot3 (see PyFAI documentation for details) in radians | [optional] [default to 0.0]
 **unit_cell** | [**UnitCell**](UnitCell.md) |  | [optional] 
 **spot_finding** | **bool** | Enable spot finding and save spots | [optional] [default to True]
+**smargon** | [**DatasetSettingsSmargon**](DatasetSettingsSmargon.md) |  | [optional] 
 **max_spot_count** | **int** | Maximum number of spots that are saved/used for indexing; spots with highest intensity are selected | [optional] [default to 250]
 **detect_ice_rings** | **bool** | Flag spots as ice rings and reduce their effect on indexing | [optional] 
 **async_start** | **bool** | When set to true, `/start` will not wait for detector and Jungfraujoch to be ready for the measurement. | [optional] [default to False]

docs/python_client/docs/DatasetSettingsSmargon.md

@@ -0,0 +1,33 @@
+# DatasetSettingsSmargon
+
+Geometry of Smargon goniometer at SLS 2.0 / MX beamlines.  Assuming that Smargon is used as static positioner and not moving during the scan, allowing to reconstruct geometry. 
+
+## Properties
+
+Name | Type | Description | Notes
+------------ | ------------- | ------------- | -------------
+**phi_deg** | **float** | Phi angle in degrees | 
+**chi_deg** | **float** | Chi angle in degrees | 
+**phi_axis** | **List[float]** | Phi rotation axis (defaults to the omega axis) | [optional] 
+**chi_axis** | **List[float]** | Chi rotation axis | [optional] 
+
+## Example
+
+```python
+from jfjoch_client.models.dataset_settings_smargon import DatasetSettingsSmargon
+
+# TODO update the JSON string below
+json = "{}"
+# create an instance of DatasetSettingsSmargon from a JSON string
+dataset_settings_smargon_instance = DatasetSettingsSmargon.from_json(json)
+# print the JSON string representation of the object
+print(DatasetSettingsSmargon.to_json())
+
+# convert the object into a dict
+dataset_settings_smargon_dict = dataset_settings_smargon_instance.to_dict()
+# create an instance of DatasetSettingsSmargon from a dict
+dataset_settings_smargon_from_dict = DatasetSettingsSmargon.from_dict(dataset_settings_smargon_dict)
+```
+[[Back to Model list]](../README.md#documentation-for-models) [[Back to API list]](../README.md#documentation-for-api-endpoints) [[Back to README]](../README.md)
+
+