feat(D): OCC mesh attribute extraction + Blender smooth shading integration

Migration 039: cad_files.mesh_attributes JSONB column.
domains/products/tasks.py: extract_mesh_attributes Celery task using pythonOCC.
still_render.py + turntable_render.py: _apply_mesh_attributes() sets auto-smooth
based on curved_ratio and topology threshold from OCC analysis.
render_blender.py: passes --mesh-attributes JSON arg to Blender subprocess.
render_still_task: loads mesh_attributes from DB and passes to renderer.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

render-worker/scripts/turntable_render.py

@@ -157,6 +157,28 @@ def _scale_mm_to_m(parts):
     print(f"[turntable_render] scaled {len(parts)} parts mm→m (×0.001)")
 
 
+def _apply_mesh_attributes(objects: list, mesh_attributes: dict) -> None:
+    """Apply topology-based shading settings from OCC analysis."""
+    import math
+    if not mesh_attributes or mesh_attributes.get("error"):
+        return
+
+    curved_ratio = mesh_attributes.get("curved_ratio", 0.0)
+    threshold_deg = mesh_attributes.get("sharp_angle_threshold_deg", 30.0)
+    threshold_rad = threshold_deg * math.pi / 180.0
+
+    for obj in objects:
+        if obj.type != 'MESH':
+            continue
+        # Enable smooth shading for predominantly curved parts (bearings etc.)
+        if curved_ratio > 0.3:
+            for poly in obj.data.polygons:
+                poly.use_smooth = True
+        # Auto-smooth at topology threshold
+        obj.data.use_auto_smooth = True
+        obj.data.auto_smooth_angle = threshold_rad
+
+
 def _import_stl(stl_file):
     """Import STL into Blender, using per-part STLs if available.
 
@@ -351,6 +373,15 @@ def main():
     bg_color = args[21] if len(args) > 21 else ""
     transparent_bg = args[22] == "1" if len(args) > 22 else False
 
+    # Named argument: --mesh-attributes <json>
+    _mesh_attrs: dict = {}
+    if "--mesh-attributes" in argv:
+        _idx = argv.index("--mesh-attributes")
+        try:
+            _mesh_attrs = json.loads(argv[_idx + 1])
+        except Exception:
+            pass
+
     os.makedirs(frames_dir, exist_ok=True)
 
     try:
@@ -402,6 +433,8 @@ def main():
         _scale_mm_to_m(parts)
         # Apply render position rotation before material/camera setup
         _apply_rotation(parts, rotation_x, rotation_y, rotation_z)
+        # Apply OCC topology-based shading overrides
+        _apply_mesh_attributes(parts, _mesh_attrs)
 
         # Move imported parts into target collection
         for part in parts:
@@ -480,6 +513,8 @@ def main():
         _scale_mm_to_m(parts)
         # Apply render position rotation before material/camera setup
         _apply_rotation(parts, rotation_x, rotation_y, rotation_z)
+        # Apply OCC topology-based shading overrides
+        _apply_mesh_attributes(parts, _mesh_attrs)
 
         for i, part in enumerate(parts):
             _apply_smooth(part, SMOOTH_ANGLE)