fix: material override pipeline — pass --material-override CLI arg to Blender scripts

The initial implementation only overrode the material_map dict in the task,
but the Blender USD primvar path bypassed it. Now:
- Added --material-override named CLI arg parsed in _blender_args.py
- Both Mode A (factory) and Mode B (template) in _blender_scene_setup.py
  override usd_material_lookup and material_map when set
- Passed through full chain: task → step_processor → render_blender → CLI → Blender
- Tested: 175-part bearing rendered with single Steel-Bare material (1/1 materials)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/domains/pipeline/tasks/render_order_line.py

@@ -201,8 +201,16 @@ def render_order_line_task(self, order_line_id: str):
             # Apply global material override from OutputType (e.g. x-ray mode)
             if line.output_type and line.output_type.material_override:
                 override_mat = line.output_type.material_override
-                material_map = {k: override_mat for k in material_map}
-                emit(order_line_id, f"Material override active: all parts → {override_mat}")
+                # Build override map from existing material_map keys or from parsed STEP parts
+                override_keys = set()
+                if material_map:
+                    override_keys = set(material_map.keys())
+                if cad_file and cad_file.parsed_objects:
+                    for part_name in cad_file.parsed_objects.get("objects", []):
+                        override_keys.add(part_name)
+                material_map = {k: override_mat for k in override_keys}
+                use_materials = True
+                emit(order_line_id, f"Material override active: {len(material_map)} parts → {override_mat}")
 
             if template:
                 emit(order_line_id, f"Using render template: {template.name} (collection={template.target_collection}, material_replace={template.material_replace_enabled}, lighting_only={template.lighting_only})")
@@ -352,6 +360,7 @@ def render_order_line_task(self, order_line_id: str):
                         usd_path=usd_render_path,
                         focal_length_mm=focal_length_mm,
                         sensor_width_mm=sensor_width_mm,
+                        material_override=line.output_type.material_override if line.output_type else None,
                     )
                     success = True
                     render_log = {
@@ -410,6 +419,7 @@ def render_order_line_task(self, order_line_id: str):
                     rotation_z=rotation_z,
                     focal_length_mm=focal_length_mm,
                     sensor_width_mm=sensor_width_mm,
+                    material_override=line.output_type.material_override if line.output_type else None,
                     job_id=order_line_id,
                     order_line_id=order_line_id,
                     noise_threshold=noise_threshold,