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/domains/billing/schemas.py

@@ -3,7 +3,7 @@ from __future__ import annotations
 import uuid
 from datetime import date, datetime
 from decimal import Decimal
-from pydantic import BaseModel
+from pydantic import BaseModel, computed_field
 
 
 class InvoiceLineCreate(BaseModel):
@@ -54,4 +54,11 @@ class InvoiceOut(BaseModel):
     created_at: datetime
     lines: list[InvoiceLineOut] = []
 
+    @computed_field  # type: ignore[misc]
+    @property
+    def pdf_url(self) -> str | None:
+        if self.pdf_key:
+            return f"/api/billing/invoices/{self.id}/pdf"
+        return None
+
     model_config = {"from_attributes": True}