v0.1.0

First release. The calibration is complete and covered by tests; validation on
real hardware is still in progress, so treat this version as field-testable
rather than proven. The error budget in docs/design/calibration-method.md is
argued from soil physics, not measured on a probe in the ground.

Added

• Calibration of a cheap capacitive soil probe against a water deficit produced
  by another integration, over repeated irrigation-to-dry-down cycles. Five
  complete cycles by default before anything is published.
• A single integration entry holding every probe of the installation, with
  probes added, edited and removed from its options, one device each.
• Automatic discovery of the companion entities on the probe's device: the
  temperature channel used as liveness sentinel, the battery, and the
  device-side calibration knobs, which are read and monitored but never written
  unless write-back is enabled explicitly.
• Seven entities per probe: calibrated soil moisture, calibration status,
  progress, complete cycles, drift, required depletion, probe online and
  calibration problem. One summary entity on the hub.
• Five services: calibrate_now, reset_calibration, mark_field_capacity,
  apply_device_offset and export_samples, addressed by probe name.
• A repair that fires when the irrigation regime waters too often for any cycle
  to count, naming the depletion configured, the depletion required, and the
  value to set.
• Metric and imperial units for the deficit and the root depth, English and
  Italian translations, and a diagnostics download.

Notes

• The calibration domain imports nothing from Home Assistant and is verified by
  a dedicated job that installs pytest alone.
• The integration declares no Python requirements: the robust estimator is
  standard library only.