refactor(B1): migrate to domain-driven project structure

Move all models/schemas/services/routers into app/domains/.
Keep backward-compat shims in old locations for imports.
Preserves domains/rendering/tasks.py from Phase A.

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

backend/app/models/__init__.py

@@ -1,20 +1,22 @@
-from app.models.user import User
-from app.models.template import Template
-from app.models.cad_file import CadFile
-from app.models.order import Order
-from app.models.order_item import OrderItem
-from app.models.audit_log import AuditLog
-from app.models.pricing_tier import PricingTier
-from app.models.product import Product
-from app.models.output_type import OutputType
-from app.models.order_line import OrderLine
-from app.models.render_template import RenderTemplate
-from app.models.material import Material
-from app.models.material_alias import MaterialAlias
-from app.models.render_position import ProductRenderPosition
+"""Re-export all models from domain locations.
+
+This file ensures that `from app.models import X` continues to work.
+The canonical definitions live in app/domains/*/models.py.
+"""
+from app.domains.auth.models import User
+from app.domains.imports.models import Template
+from app.domains.products.models import CadFile, Product
+from app.domains.orders.models import Order, OrderItem, OrderLine
+from app.domains.notifications.models import AuditLog
+from app.domains.billing.models import PricingTier
+from app.domains.rendering.models import OutputType, RenderTemplate, ProductRenderPosition
+from app.domains.materials.models import Material, MaterialAlias
+
+# Also re-export SystemSetting (no domain assigned — stays as-is)
+from app.models.system_setting import SystemSetting
 
 __all__ = [
-    "User", "Template", "CadFile", "Order", "OrderItem", "AuditLog",
-    "PricingTier", "Product", "OutputType", "OrderLine",
-    "RenderTemplate", "Material", "MaterialAlias", "ProductRenderPosition",
+    "User", "Template", "CadFile", "Product", "Order", "OrderItem", "OrderLine",
+    "AuditLog", "PricingTier", "OutputType", "RenderTemplate", "ProductRenderPosition",
+    "Material", "MaterialAlias", "SystemSetting",
 ]