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/render_position.py

@@ -1,28 +1,3 @@
-import uuid
-from datetime import datetime
-from sqlalchemy import String, DateTime, Boolean, Integer, Float, ForeignKey
-from sqlalchemy.orm import Mapped, mapped_column, relationship
-from sqlalchemy.dialects.postgresql import UUID
-from app.database import Base
-
-
-class ProductRenderPosition(Base):
-    __tablename__ = "product_render_positions"
-
-    id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
-    product_id: Mapped[uuid.UUID] = mapped_column(
-        UUID(as_uuid=True), ForeignKey("products.id", ondelete="CASCADE"), nullable=False, index=True
-    )
-    name: Mapped[str] = mapped_column(String(200), nullable=False)
-    rotation_x: Mapped[float] = mapped_column(Float, nullable=False, default=0.0)
-    rotation_y: Mapped[float] = mapped_column(Float, nullable=False, default=0.0)
-    rotation_z: Mapped[float] = mapped_column(Float, nullable=False, default=0.0)
-    is_default: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False)
-    sort_order: Mapped[int] = mapped_column(Integer, nullable=False, default=0)
-    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
-    )
-
-    product: Mapped["Product"] = relationship("Product", back_populates="render_positions")
-    order_lines: Mapped[list["OrderLine"]] = relationship("OrderLine", back_populates="render_position")
+# Compat shim — use app.domains.rendering.models instead
+from app.domains.rendering.models import ProductRenderPosition
+__all__ = ["ProductRenderPosition"]