Unitree H1: sync body masses and inertials with upstream URDF update

[akushonkamen]

Description

unitree_h1/h1.xml still carried the pre-Dec-2025 body inertials. Upstream
unitreerobotics/unitree_ros@34e7506
(2025-12-31, "update h1 urdf (mass&inertial)") revised the masses, centers of mass and
inertia tensors of the pelvis, both legs and both arms — 59.34 kg total — while h1.xml
summed to 51.44 kg, the discrepancy reported in #333.

The fix resyncs the affected <inertial> blocks from that URDF commit via a scripted
URDF→MJCF conversion (R_rpy @ I @ R_rpy^T, eigen-decomposition into the principal frame),
applied minimally:

• pelvis + all 10 leg links: mass, COM and inertia fully resynced
• 6 arm links: mass only (COM and inertia already matched)
• 2 elbow links: pos + mass (stale COM, inertia matched)
• torso_link untouched (already matched)

Joint limits, kinematics and collision geometry are unchanged; the hip_pitch range is
left as-is per the open question in the issue. unitree_h1/CHANGELOG.md documents the
change and the contributor entry is added to CONTRIBUTORS.md (alphabetical by first name,
per the sorted-order test).

Methodology check: before being applied, the converter was validated to reproduce the
then-current file's (parent revision, unitree_ros e909ca2) masses, COMs and diagonal
inertias digit-for-digit.

Verification, all run locally on this exact tree:

• RED, before patch: XML-level checker comparing every body against the
  unitree_ros@34e7506 URDF → 19/20 bodies FAIL, totals mjcf=51.437 vs urdf=59.338
  (reproduces the issue's 51.44/59.34).
• GREEN, after patch: same checker → checked=20 failures=0, totals equal at 59.338.
• Compiled-model checker (MuJoCo 3.16.0): reconstructed mass, COM and body-frame inertia
  of all 20 bodies match the URDF; total model mass 59.338 kg.
• make check: all pre-commit hooks Passed (trailing-whitespace, end-of-file, yaml,
  merge-conflict, mixed-line, ruff, ruff-format, LICENSE, format_xml).
• Full suite: uv run --quiet --with-requirements test/requirements.txt pytest test/ -q
  → 375 passed, 1 skipped.

Investigated, edited and tested with Claude Code (AI assistant).

Fixes: #333

Checklist

• make all passes locally (lint, format, license, XML, tests) — make check all
  hooks Passed; pytest test/ 375 passed, 1 skipped
• Added my name to CONTRIBUTORS.md (alphabetical by first name)
• Updated the relevant CHANGELOG.md (model-local: unitree_h1/CHANGELOG.md)
• Signed the Contributor License Agreement (CLA)
  — left unticked: signing requires the account holder's action; will be ticked once
  confirmed at cla.developers.google.com

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