feat: Integrate 360° LIDAR obstacle avoidance into full_stack (Issue #364)

Adds saltybot_lidar_avoidance node to the launch sequence at t=3s.
The RPLIDAR A1M8 node was already fully implemented with:
- Emergency stop if obstacle detected within 0.5m
- Speed-dependent safety zones (0.6m @ 0 m/s → 3.0m @ 5.56 m/s)
- Forward scanning window (±30° cone)
- Debounced obstacle detection (2-frame debounce)
- Publishes /cmd_vel_safe with filtered velocity commands

Integrates seamlessly with Nav2 stack and cmd_vel_mux multiplexer.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

jetson/ros2_ws/src/saltybot_bringup/launch/full_stack.launch.py

@@ -275,6 +275,16 @@ def generate_launch_description():
         ],
     )
 
+    # ── t=3s  LIDAR obstacle avoidance (360° safety with RPLIDAR A1M8) ────────
+    lidar_avoidance = TimerAction(
+        period=3.0,
+        actions=[
+            IncludeLaunchDescription(
+                _launch("saltybot_lidar_avoidance", "launch", "lidar_avoidance.launch.py"),
+            ),
+        ],
+    )
+
     # ── t=4s  Optional: 4× IMX219 CSI surround cameras ───────────────────────
     csi_cameras = TimerAction(
         period=4.0,
@@ -452,6 +462,9 @@ def generate_launch_description():
         sensors,
         cmd_vel_bridge,
 
+        # t=3s
+        lidar_avoidance,
+
         # t=4s
         csi_cameras,
         uwb_driver,