feat(K): Blender Asset Library + production exports (GLB + .blend)

- feat(migration): 045_asset_libraries — new asset_libraries table (blend_file_path, catalog JSONB)
- feat(model): AssetLibrary SQLAlchemy model in domains/materials/models.py
- feat(api): POST/GET/PATCH/DELETE /api/asset-libraries + /upload-blend + /refresh-catalog endpoints
- feat(celery): refresh_asset_library_catalog task on thumbnail_rendering queue — runs Blender headless
- feat(blender): catalog_assets.py — extracts asset-marked materials + node_groups from .blend
- feat(blender): asset_library.py — apply_asset_library_materials + apply_asset_library_node_groups helpers
- feat(blender): export_gltf.py — STEP→STL→GLB production export with optional asset library
- feat(blender): export_blend.py — STEP→STL→.blend production export with pack_all()
- feat(frontend): api/assetLibraries.ts — full CRUD API client
- feat(frontend): AssetLibraryPanel in Admin.tsx — upload, refresh, expand catalog view
- docs: Blender asset_data marking requirement learning in LEARNINGS.md

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

render-worker/scripts/catalog_assets.py

@@ -0,0 +1,43 @@
+"""Blender headless script: extract asset catalog from a .blend library file.
+
+Usage:
+    blender --background --python catalog_assets.py -- <blend_path>
+
+Outputs a single JSON line to stdout:
+    {"materials": ["Mat1", "Mat2", ...], "node_groups": ["NG1", ...]}
+
+Only assets marked via Blender's asset system (asset_data is not None) are included.
+"""
+from __future__ import annotations
+
+import json
+import sys
+import traceback
+
+
+def main() -> None:
+    argv = sys.argv
+    if "--" not in argv:
+        print(json.dumps({"error": "No blend path provided after --"}))
+        sys.exit(1)
+
+    blend_path = argv[argv.index("--") + 1]
+
+    import bpy  # type: ignore[import]
+
+    bpy.ops.wm.open_mainfile(filepath=blend_path)
+
+    materials = [m.name for m in bpy.data.materials if m.asset_data is not None]
+    node_groups = [ng.name for ng in bpy.data.node_groups if ng.asset_data is not None]
+
+    catalog = {"materials": materials, "node_groups": node_groups}
+    print(json.dumps(catalog))
+
+
+try:
+    main()
+except SystemExit:
+    raise
+except Exception:
+    traceback.print_exc()
+    sys.exit(1)