fix: replace the default factory calibration with measured values

[cao-xiao-hao]

Summary

src/litegrip/factory_calibration.json is the last entry of the automatic load
chain, so it is what an uncalibrated unit runs on. Its numbers were nominal for a
120 mm stroke unit (1.605 rad × 74.8 mm/rad); the measured unit travels 86.0 mm
over 1.409552 rad. This replaces the file with the measured values.

Two things a reviewer should see before merging:

• This breaks the default travel for existing consumers. Anyone relying on the
  built-in fallback gets a different stroke (120 mm → 86.0 mm) and a different
  rad_to_mm (74.8 → 61.01229326764816) without changing their code. Under the
  version policy this ships as a patch (fix:), not a major — no BREAKING CHANGE:
  was approved. Say so now if it should be a major.
• kp drops from 100.0 to 5.0. The field is carried by the file and
  load_calibration() applies it to GripperConfig, so it overrides
  GripperParams.DEFAULT_KP on the fallback path — a 20× softer grip. If 5.0 is
  a value measured for one bench setup rather than the shipped default, drop that
  line before merging.

Changes

• src/litegrip/factory_calibration.json: zero_position_rad 0.114 → 0.052071,
  max_position_rad -1.491 → -1.357481, travel_range_rad 1.605 → 1.409552,
  rad_to_mm 74.8 → 61.01229326764816, kp 100.0 → 5.0.
• Everything else (channel, can_id, mst_id, canfd_mode, motor_type, kd,
  grasp_torque_threshold) is unchanged.
• No code or documentation change: the README describes the factory file as a normal
  mount without quoting its numbers, and the ordering of the limits still makes it a
  normal mount (0.052071 > -1.357481), so mount still reads "normal" and the
  template fallback guard still holds.

Testing

Baseline before the change, and again after it — same result:

$ python3 -m unittest discover -s tests -t tests -v
----------------------------------------------------------------------
Ran 105 tests in 1.720s

OK

Loaded the new file directly to confirm the derived values:

$ PYTHONPATH=src python3 -c "from litegrip import LiteGrip; from litegrip.gripper import _FACTORY_CALIB; g=LiteGrip('can0'); print(g.load_calibration(_FACTORY_CALIB))"
True

mount = normal, pos_closed_rad = 0.052071, pos_open_rad = -1.357481,
rad_to_mm = 61.01229326764816, kp, kd = 5.0 2.0, calibrated = True,
stroke_mm = 86.0.

The data is internally consistent: 1.409552 × 61.01229326764816 = 86.0000, which
matches travel_range_rad and the two limits (0.052071 - (-1.357481) = 1.409552).

Issues

None.

[github-actions]

🎉 This PR is included in version 0.5.1 🎉

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