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>

backend/app/domains/materials/models.py

@@ -1,8 +1,8 @@
 import uuid
 from datetime import datetime
-from sqlalchemy import String, DateTime, Text, ForeignKey, Integer
+from sqlalchemy import String, DateTime, Text, ForeignKey, Integer, Boolean
 from sqlalchemy.orm import Mapped, mapped_column, relationship
-from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.dialects.postgresql import UUID, JSONB
 from app.database import Base
 # TYPE_CHECKING import to avoid circular references
 from typing import TYPE_CHECKING
@@ -45,3 +45,20 @@ class MaterialAlias(Base):
     created_at: Mapped[datetime] = mapped_column(DateTime, default=datetime.utcnow, nullable=False)
 
     material = relationship("Material", back_populates="aliases")
+
+
+class AssetLibrary(Base):
+    __tablename__ = "asset_libraries"
+
+    id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    tenant_id: Mapped[uuid.UUID | None] = mapped_column(
+        UUID(as_uuid=True), ForeignKey("tenants.id", ondelete="SET NULL"), nullable=True, index=True
+    )
+    name: Mapped[str] = mapped_column(String(200), nullable=False)
+    blend_file_path: Mapped[str | None] = mapped_column(Text, nullable=True)
+    original_filename: Mapped[str | None] = mapped_column(String(500), nullable=True)
+    catalog: Mapped[dict] = mapped_column(JSONB, nullable=False, default=lambda: {"materials": [], "node_groups": []})
+    description: Mapped[str | None] = mapped_column(Text, nullable=True)
+    is_active: Mapped[bool] = mapped_column(Boolean, nullable=False, default=True)
+    created_at: Mapped[datetime] = mapped_column(DateTime, default=datetime.utcnow, nullable=False)
+    updated_at: Mapped[datetime] = mapped_column(DateTime, default=datetime.utcnow, onupdate=datetime.utcnow, nullable=False)