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>

frontend/src/pages/Billing.tsx

@@ -3,7 +3,7 @@ import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query'
 import { Receipt, Download, Trash2, Plus, X } from 'lucide-react'
 import { toast } from 'sonner'
 import {
-  getInvoices, createInvoice, updateInvoiceStatus, deleteInvoice, getInvoicePdfUrl,
+  getInvoices, createInvoice, updateInvoiceStatus, deleteInvoice, downloadInvoicePdf,
   type Invoice, type InvoiceCreate,
 } from '../api/billing'
 
@@ -196,15 +196,13 @@ export default function BillingPage() {
                 <td className="px-4 py-3 text-sm text-content-secondary">{formatDate(inv.due_at)}</td>
                 <td className="px-4 py-3 text-sm text-content">{formatCurrency(inv.total_net, inv.currency)}</td>
                 <td className="px-4 py-3 flex items-center gap-1">
-                  <a
-                    href={getInvoicePdfUrl(inv.id)}
-                    target="_blank"
-                    rel="noopener noreferrer"
+                  <button
+                    onClick={() => downloadInvoicePdf(inv.id).catch(() => toast.error('PDF download failed'))}
                     className="p-1.5 rounded hover:bg-gray-200 text-gray-500 hover:text-gray-700 transition-colors"
                     title="Download PDF"
                   >
                     <Download size={15} />
-                  </a>
+                  </button>
                   {inv.status === 'draft' && (
                     <button
                       onClick={() => {