LaserSafetyFilter: scan-based emergency brake + evasive turn before cmd publish

include/car_nav_lite/laser_safety.hpp

@@ -0,0 +1,20 @@
+#pragma once
+
+#include "car_nav_lite/types.hpp"
+
+namespace car_nav_lite {
+
+// Fast scan-based safety filter. Runs every frame before publishing cmd_vel.
+// Checks if the planned command would hit anything in the latest scan.
+struct LaserSafetyFilter {
+    bool enable = true;
+    double front_width = 0.30;   // half-width of front safety zone (m)
+    double stop_dist  = 0.35;   // brake distance (m)
+    double slow_dist  = 0.70;   // slow-down distance (m)
+    double turn_wz    = 0.8;    // evasive turn rate (rad/s)
+    double max_range  = 2.0;    // max lookahead (m)
+
+    Twist filter(const Twist& cmd, const LaserScan& scan) const;
+};
+
+}  // namespace car_nav_lite