Add G20 calibration assets, L20 compare, and refresh README.

Sync calibrated G20 URDF/MJCF/JSON lookup, L20 V10.1 dual-compare scripts,
joint GUI, and document O6/G20/L20 startup on the Gitea repo.

Co-authored-by: Cursor <cursoragent@cursor.com>

run_g20_joint_gui.sh

@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+# G20 关节弧度监视 GUI（默认 6 位小数）
+# 订阅 /sim/mujoco/g20/left/joint_state
+set -eo pipefail
+ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+cd "$ROOT"
+
+set +u
+# shellcheck disable=SC1091
+source /opt/ros/jazzy/setup.bash
+if [[ -f "$ROOT/install/setup.bash" ]]; then
+  # shellcheck disable=SC1091
+  source "$ROOT/install/setup.bash"
+fi
+set -u
+
+VENV_SITE="$ROOT/venv/lib/python3.12/site-packages"
+if [[ -d "$VENV_SITE" ]]; then
+  export PYTHONPATH="$VENV_SITE${PYTHONPATH:+:$PYTHONPATH}"
+fi
+
+PKG_SRC="$ROOT/src/linkerhand-sim/linker_hand_mujoco_ros2"
+export PYTHONPATH="$PKG_SRC${PYTHONPATH:+:$PYTHONPATH}"
+
+exec python3 -m linker_hand_mujoco_ros2.g20_joint_monitor_gui "$@"