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/cad_file.py

@@ -1,37 +1,3 @@
-import uuid
-from datetime import datetime
-from sqlalchemy import String, DateTime, Enum as SAEnum, BigInteger
-from sqlalchemy.orm import Mapped, mapped_column, relationship
-from sqlalchemy.dialects.postgresql import UUID, JSONB
-from app.database import Base
-import enum
-
-
-class ProcessingStatus(str, enum.Enum):
-    pending = "pending"
-    processing = "processing"
-    completed = "completed"
-    failed = "failed"
-
-
-class CadFile(Base):
-    __tablename__ = "cad_files"
-
-    id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
-    original_name: Mapped[str] = mapped_column(String(500), nullable=False)
-    stored_path: Mapped[str] = mapped_column(String(1000), nullable=False)
-    file_hash: Mapped[str] = mapped_column(String(64), unique=True, nullable=False, index=True)
-    file_size: Mapped[int] = mapped_column(BigInteger, nullable=True)
-    parsed_objects: Mapped[dict] = mapped_column(JSONB, nullable=True)
-    thumbnail_path: Mapped[str] = mapped_column(String(1000), nullable=True)
-    gltf_path: Mapped[str] = mapped_column(String(1000), nullable=True)
-    processing_status: Mapped[ProcessingStatus] = mapped_column(
-        SAEnum(ProcessingStatus), default=ProcessingStatus.pending, nullable=False
-    )
-    error_message: Mapped[str] = mapped_column(String(2000), nullable=True)
-    render_log: Mapped[dict] = mapped_column(JSONB, nullable=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)
-
-    order_items: Mapped[list["OrderItem"]] = relationship("OrderItem", back_populates="cad_file")
-    products: Mapped[list["Product"]] = relationship("Product", back_populates="cad_file")
+# Compat shim — use app.domains.products.models instead
+from app.domains.products.models import CadFile, ProcessingStatus
+__all__ = ["CadFile", "ProcessingStatus"]