Add robot definition URDF

This enables rviz2 to know where sensors etc are.
None of the data is correct for the raspbot-v2 yet.

robot/src/raspbot_v2/launch/robot.launch.py

@@ -1,10 +1,22 @@
+import os
+
+from ament_index_python.packages import get_package_share_directory
 from launch import LaunchDescription
 from launch.actions import DeclareLaunchArgument
-from launch.substitutions import LaunchConfiguration
+from launch.substitutions import LaunchConfiguration, Command
 from launch_ros.actions import Node
+from launch_ros.parameter_descriptions import ParameterValue
 
 
 def generate_launch_description():
+    urdf_file = os.path.join(
+        get_package_share_directory('raspbot_v2'), 'urdf', 'raspbot_v2.urdf.xacro'
+    )
+    robot_description = ParameterValue(
+        Command(['xacro ', urdf_file]),
+        value_type=str,
+    )
+
     return LaunchDescription([
 
         # ── Motor controller arguments ────────────────────────────────────
@@ -23,6 +35,33 @@ def generate_launch_description():
         DeclareLaunchArgument('tilt_center_deg', default_value='60.0',
                               description='Tilt angle at startup and shutdown (degrees)'),
 
+        # ── TF / robot description ────────────────────────────────────────
+        Node(
+            package='robot_state_publisher',
+            executable='robot_state_publisher',
+            name='robot_state_publisher',
+            parameters=[{'robot_description': robot_description}],
+            output='screen',
+        ),
+
+        # Static: map → odom (identity — replace with SLAM/AMCL when ready)
+        Node(
+            package='tf2_ros',
+            executable='static_transform_publisher',
+            name='map_to_odom',
+            arguments=['0', '0', '0', '0', '0', '0', 'map', 'odom'],
+            output='screen',
+        ),
+
+        # Static: odom → base_footprint (placeholder until odometry is added)
+        Node(
+            package='tf2_ros',
+            executable='static_transform_publisher',
+            name='odom_to_base',
+            arguments=['0', '0', '0', '0', '0', '0', 'odom', 'base_footprint'],
+            output='screen',
+        ),
+
         # ── Nodes ─────────────────────────────────────────────────────────
         Node(
             package='raspbot_v2',