Fix ambient lighting intensity in capture_360_images (#566)

The ambient_intensity parameter in lighting_config was not being properly
applied during 360-degree image capture. This change ensures that the
directional light intensity scales with the ambient_intensity value,
making brightness adjustments work as expected.

- Scale DirectionalLight intensity with ambient_intensity parameter
- Improve ambient light reset in cleanup method

Author: iory

skrobot/viewers/_pyrender.py

@@ -505,7 +505,9 @@ def _setup_scene_lighting(self, lighting_config=None):
                                                  ambient_intensity])
 
             # Add a single directional light for some definition
-            light = pyrender.DirectionalLight(color=[1.0, 1.0, 1.0], intensity=0.2)
+            # Scale its intensity with ambient_intensity
+            light = pyrender.DirectionalLight(color=[1.0, 1.0, 1.0],
+                                              intensity=ambient_intensity * 2.0)
             pose = np.eye(4)
             # Point downward from above
             pose[:3, :3] = transformations.euler_matrix(np.pi / 4, 0, 0)[:3, :3]
@@ -544,7 +546,7 @@ def _cleanup_scene_lighting(self, light_nodes):
         for light_node in light_nodes:
             self.scene.remove_node(light_node)
         # Reset ambient light to default
-        self.scene.ambient_light = None
+        self.scene.ambient_light = np.array([0., 0., 0.])
 
     def _update_scene_meshes(self):
         """Update scene meshes with latest transforms."""