refactor: remove dead export_gltf.py, cleanup rendering tasks, improve tessellation UI

- Remove export_gltf.py (Blender-based GLB export replaced by OCC direct)
- Remove unused export_gltf_for_order_line_task
- Add Ultra tessellation preset to Admin settings
- Improve tessellation preset descriptions and styling
- Minor cleanup across media, rendering, and workflow modules

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

backend/app/domains/media/router.py

@@ -142,7 +142,6 @@ async def browse_media_assets(
     # Apply filters
     _TECHNICAL_TYPES = (
         MediaAssetType.gltf_geometry,
-        MediaAssetType.gltf_production,
         MediaAssetType.blend_production,
         MediaAssetType.stl_low,
         MediaAssetType.stl_high,