Add LinkerHand Isaac Sim bridge and G20 assets.

Includes G20 PLAN/cmd_u8 bridge, joint mapping, dual-hand sim scripts,
and G20/L20/O6 URDF with USD payloads for Isaac Sim integration.

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

run_ui.sh

@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+# 启动 O6/G20 关节控制 UI（系统 ROS2 + tkinter，不要用 Isaac python.sh）
+set -eo pipefail
+
+# ROS setup.bash 会读未定义变量，不能在 set -u 下 source
+if [[ -f /opt/ros/jazzy/setup.bash ]]; then
+  # shellcheck disable=SC1091
+  source /opt/ros/jazzy/setup.bash
+elif [[ -f /opt/ros/humble/setup.bash ]]; then
+  # shellcheck disable=SC1091
+  source /opt/ros/humble/setup.bash
+else
+  echo "未找到 ROS2 setup.bash（jazzy/humble）" >&2
+  exit 1
+fi
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+exec python3 "$SCRIPT_DIR/hand_control_ui.py" "$@"