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/alembic/versions/045_asset_libraries.py

@@ -0,0 +1,34 @@
+"""asset_libraries table
+
+Revision ID: 045
+Revises: 044
+Create Date: 2026-03-06
+"""
+from alembic import op
+import sqlalchemy as sa
+from sqlalchemy.dialects.postgresql import UUID, JSONB
+
+revision = "045"
+down_revision = "044"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "asset_libraries",
+        sa.Column("id", UUID(as_uuid=True), primary_key=True, server_default=sa.text("gen_random_uuid()")),
+        sa.Column("tenant_id", UUID(as_uuid=True), sa.ForeignKey("tenants.id", ondelete="SET NULL"), nullable=True, index=True),
+        sa.Column("name", sa.String(200), nullable=False),
+        sa.Column("blend_file_path", sa.Text, nullable=True),
+        sa.Column("original_filename", sa.String(500), nullable=True),
+        sa.Column("catalog", JSONB, nullable=False, server_default='{"materials": [], "node_groups": []}'),
+        sa.Column("description", sa.Text, nullable=True),
+        sa.Column("is_active", sa.Boolean, nullable=False, server_default="true"),
+        sa.Column("created_at", sa.DateTime, nullable=False, server_default=sa.text("now()")),
+        sa.Column("updated_at", sa.DateTime, nullable=False, server_default=sa.text("now()")),
+    )
+
+
+def downgrade() -> None:
+    op.drop_table("asset_libraries")