docs: publish the powder calibration schemas in the python client docs

docs/python_client is tracked and is what readthedocs publishes, but it is
generated - update_version.sh copies it out of python-client after regenerating
the client - so adding schemas to the spec left it four files behind. The
README's model list did not name them and their pages did not exist.

Copied the way update_version.sh copies them. The four new pages and four lines
in the README, nothing else: the generator's README is built from the spec, so
the stale Calibration* pages it had left on disk under the old names are absent
from it and were removed before copying rather than published alongside their
replacements.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NfuDvf5ipV3Hi8TiCUKD27

docs/python_client/README.md

@@ -211,6 +211,10 @@ Class | Method | HTTP request | Description
  - [Plot](docs/Plot.md)
  - [PlotUnitX](docs/PlotUnitX.md)
  - [Plots](docs/Plots.md)
+ - [PowderCalibrationFitSigma](docs/PowderCalibrationFitSigma.md)
+ - [PowderCalibrationOutput](docs/PowderCalibrationOutput.md)
+ - [PowderCalibrationQuality](docs/PowderCalibrationQuality.md)
+ - [PowderCalibrationSpotCheck](docs/PowderCalibrationSpotCheck.md)
  - [RoiAzimList](docs/RoiAzimList.md)
  - [RoiAzimuthal](docs/RoiAzimuthal.md)
  - [RoiBox](docs/RoiBox.md)