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/rendering/workflow_builder.py

@@ -64,23 +64,16 @@ def _build_multi_angle(order_line_id: str, params: dict):
 
 
 def _build_still_with_exports(order_line_id: str, params: dict):
-    """Still render + parallel GLB exports (geometry + production quality).
+    """Still render + .blend export.
 
     Pipeline:
-        render_order_line_still_task → group(
-            export_gltf_for_order_line_task,
-            export_blend_for_order_line_task,
-        )
+        render_order_line_still_task → export_blend_for_order_line_task
     """
     from app.domains.rendering.tasks import (
         render_order_line_still_task,
-        export_gltf_for_order_line_task,
         export_blend_for_order_line_task,
     )
     return chain(
         render_order_line_still_task.si(order_line_id, **params),
-        group(
-            export_gltf_for_order_line_task.si(order_line_id),
-            export_blend_for_order_line_task.si(order_line_id),
-        ),
+        export_blend_for_order_line_task.si(order_line_id),
     )