MPPI planner + fence-line localization + scan obstacles

- Lightweight MPPI (200 trajectories, 15 steps, endpoint path_align)
- adaptive exploration (more random when stuck)
- fence-line Hough detection + geometric correction
- scan hit points marked at 255 immediately
- forward half-step pre-check for obstacle avoidance
- Ackermann constraint |wz| <= |vx|/min_turn_r
- XORshift RNG (stdlib broken on ARM)

launch/nav_lite.launch.py

@@ -0,0 +1,31 @@
+from launch import LaunchDescription
+from launch.actions import DeclareLaunchArgument
+from launch.substitutions import LaunchConfiguration
+from launch_ros.actions import Node
+
+def generate_launch_description():
+    return LaunchDescription([
+        DeclareLaunchArgument("map_file", default_value="/home/cyy/sim_map.pgm"),
+        DeclareLaunchArgument("lookahead", default_value="0.8"),
+        DeclareLaunchArgument("test_mode", default_value="false"),
+
+        # Static TF: base_link → laser
+        Node(
+            package="tf2_ros", executable="static_transform_publisher",
+            name="tf_laser",
+            arguments=["0","0","0.12","0","0","0","base_link","laser"],
+        ),
+
+        # Main navigation node
+        Node(
+            package="car_nav_lite",
+            executable="nav_lite_node",
+            name="nav_lite_node",
+            output="screen",
+            parameters=[{
+                "map_file": LaunchConfiguration("map_file"),
+                "lookahead": LaunchConfiguration("lookahead"),
+                "test_mode": LaunchConfiguration("test_mode"),
+            }],
+        ),
+    ])