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/template.py

@@ -1,24 +1,3 @@
-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")
+# Compat shim — use app.domains.imports.models instead
+from app.domains.imports.models import Template
+__all__ = ["Template"]