Fix NaN artifacts in tif_to_crop tile rendering

Replace NaN values with 0 before colormap application so no-data
zones render as the darkest color instead of undefined pixels.

lidar_pipeline/rendering.py

@@ -840,6 +840,9 @@ def tif_to_crop(tif_file, vis_dir, resolution, keep_tif=False, quality=98, outpu
         # Apply colormap normalization
         data, cmap_name, title, legend_label, description, is_rgb_result = _apply_colormap(data, tif_file, resolution=resolution)
 
+        if not is_rgb_result:
+            data = np.where(np.isnan(data), 0.0, data)
+
         # Convert to RGB using colormap
         if is_rgb_result:
             # RGB images are already in RGB (uint8 depuis le TIF IGN, ou float 0-1)