feat: layout hamburger, media browser filters+previews, billing fixes

- Layout: mobile hamburger menu + overlay backdrop + close button; content area always full-width
- Media browser: filter chips (default still+turntable); advanced toggle for GLB/STL; thumbnail_url previews for non-image types; video hover-play for turntable
- Backend: asset_types multi-filter, thumbnail_url in MediaAssetOut, download proxy endpoint for MinIO/local files
- Admin: "Import Existing Media" button → POST /api/admin/import-media-assets
- Billing: fix invoice create 500 (MissingGreenlet — use selectinload after commit); PDF download uses axios blob instead of bare <a href> (auth header missing); fix storage.upload() accepting str|Path
- SSE task logs: task_logs.py core + router, LiveRenderLog component
- CadPreview: fix infinite loop when no gltf_geometry assets; loading screen before ThreeDViewer render
- render-worker: add trimesh layer to Dockerfile

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

backend/app/main.py

@@ -24,6 +24,7 @@ from app.domains.rendering.workflow_router import router as workflows_router
 from app.domains.media.router import router as media_router
 from app.api.routers.asset_libraries import router as asset_libraries_router
 from app.domains.admin.dashboard_router import router as dashboard_router
+from app.api.routers.task_logs import router as task_logs_router
 
 
 @asynccontextmanager
@@ -90,6 +91,7 @@ app.include_router(workflows_router)
 app.include_router(media_router)
 app.include_router(asset_libraries_router, prefix="/api")
 app.include_router(dashboard_router, prefix="/api")
+app.include_router(task_logs_router, prefix="/api")
 
 
 @app.get("/health")