chore: 框架科学优化前的完整基线

在开始'设备契约层 + 目录重构 + 通止规装配'改造之前，先钉住当前可运行状态，
使后续任何删除/重构都可回退。

本基线包含：
- 现有 ROS 2 工作区全部源码（arm_application / arm_control / arm_bringup 等）
- 官方 flexiv_ros2 栈（含 flexiv_hardware / flexiv_controllers 等符号链接）
- 设备契约层 src/arm_interfaces（新增，46 项单测通过）
- devices/ 设备选型与品牌清单（新增）
- scripts/gen_site_example.py 与由它生成的 config/site.example.yaml

按 .gitignore 排除：build/ / install/ / log/ / config/site.yaml / 模型权重二进制。

src/arm_description/launch/display.launch.py

@@ -0,0 +1,70 @@
+from launch import LaunchDescription
+from launch.actions import DeclareLaunchArgument
+from launch.conditions import IfCondition, UnlessCondition
+from launch.substitutions import Command, LaunchConfiguration, PathJoinSubstitution
+from launch_ros.actions import Node
+from launch_ros.parameter_descriptions import ParameterValue
+from launch_ros.substitutions import FindPackageShare
+
+
+def generate_launch_description():
+    use_gui = LaunchConfiguration('use_gui')
+    use_rviz = LaunchConfiguration('use_rviz')
+    robot_sn = LaunchConfiguration('robot_sn')
+    rizon_type = LaunchConfiguration('rizon_type')
+    load_gripper = LaunchConfiguration('load_gripper')
+
+    urdf_path = PathJoinSubstitution(
+        [FindPackageShare('arm_description'), 'urdf', 'arm.urdf.xacro']
+    )
+    rviz_config = PathJoinSubstitution(
+        [FindPackageShare('flexiv_description'), 'rviz', 'view_rizon.rviz']
+    )
+
+    robot_description = ParameterValue(
+        Command([
+            'xacro ', urdf_path,
+            ' robot_sn:=', robot_sn,
+            ' rizon_type:=', rizon_type,
+            ' load_gripper:=', load_gripper,
+        ]),
+        value_type=str,
+    )
+
+    return LaunchDescription([
+        DeclareLaunchArgument('use_gui', default_value='true'),
+        DeclareLaunchArgument('use_rviz', default_value='true'),
+        DeclareLaunchArgument('robot_sn', default_value='Rizon4-063989'),
+        DeclareLaunchArgument('rizon_type', default_value='Rizon4'),
+        DeclareLaunchArgument('load_gripper', default_value='false'),
+
+        Node(
+            package='robot_state_publisher',
+            executable='robot_state_publisher',
+            name='robot_state_publisher',
+            parameters=[{'robot_description': robot_description}],
+            output='screen',
+        ),
+        Node(
+            package='joint_state_publisher_gui',
+            executable='joint_state_publisher_gui',
+            name='joint_state_publisher_gui',
+            condition=IfCondition(use_gui),
+            output='screen',
+        ),
+        Node(
+            package='joint_state_publisher',
+            executable='joint_state_publisher',
+            name='joint_state_publisher',
+            condition=UnlessCondition(use_gui),
+            output='screen',
+        ),
+        Node(
+            package='rviz2',
+            executable='rviz2',
+            name='rviz2',
+            arguments=['-d', rviz_config],
+            condition=IfCondition(use_rviz),
+            output='screen',
+        ),
+    ])