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_router.py

@@ -51,7 +51,6 @@ _STEP_CATEGORIES: dict[StepName, StepCategory] = {
     StepName.BLENDER_STILL: "rendering",
     StepName.BLENDER_TURNTABLE: "rendering",
     StepName.OUTPUT_SAVE: "output",
-    StepName.EXPORT_GLB_GEOMETRY: "output",
     StepName.EXPORT_BLEND: "output",
     StepName.STL_CACHE_GENERATE: "processing",
     StepName.NOTIFY: "output",
@@ -72,7 +71,6 @@ _STEP_DESCRIPTIONS: dict[StepName, str] = {
     StepName.BLENDER_STILL: "Render a production still image (PNG) via Blender HTTP micro-service",
     StepName.BLENDER_TURNTABLE: "Render all turntable animation frames via Blender HTTP micro-service",
     StepName.OUTPUT_SAVE: "Upload the rendered output file to storage and create a MediaAsset record",
-    StepName.EXPORT_GLB_GEOMETRY: "Export a geometry-only GLB for the 3-D viewer (no materials)",
     StepName.EXPORT_BLEND: "Save the production .blend file as a downloadable MediaAsset",
     StepName.STL_CACHE_GENERATE: "Convert STEP → STL (low + high quality) and cache next to the STEP file",
     StepName.NOTIFY: "Emit a user notification via the audit-log notification channel",