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/domains/imports/models.py

@@ -0,0 +1,24 @@
+import uuid
+from datetime import datetime
+from sqlalchemy import String, Boolean, DateTime, Text
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+from sqlalchemy.dialects.postgresql import UUID, JSONB
+from app.database import Base
+
+
+class Template(Base):
+    __tablename__ = "templates"
+
+    id: Mapped[uuid.UUID] = mapped_column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    name: Mapped[str] = mapped_column(String(255), nullable=False)
+    category_key: Mapped[str] = mapped_column(String(100), unique=True, nullable=False, index=True)
+    # JSONB config for each of the 11 standard columns: {col_index: {label, required, optional}}
+    standard_fields: Mapped[dict] = mapped_column(JSONB, nullable=False, default=dict)
+    # JSONB schema for expected component pairs
+    component_schema: Mapped[dict] = mapped_column(JSONB, nullable=False, default=dict)
+    description: Mapped[str] = mapped_column(Text, nullable=True)
+    is_active: Mapped[bool] = mapped_column(Boolean, default=True, nullable=False)
+    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)
+
+    orders: Mapped[list["Order"]] = relationship("Order", back_populates="template")