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/services/order_service.py

@@ -1,22 +1,3 @@
-"""Order number generation and business logic."""
-from datetime import datetime
-from sqlalchemy.ext.asyncio import AsyncSession
-from sqlalchemy import select, func
-from app.models.order import Order
-
-
-async def generate_order_number(db: AsyncSession) -> str:
-    """Generate next sequential order number: SA-2026-XXXXX."""
-    year = datetime.utcnow().year
-    prefix = f"SA-{year}-"
-
-    # Use MAX to find the highest existing sequence number this year.
-    # COUNT-based approach breaks when orders are deleted (produces duplicates).
-    result = await db.execute(
-        select(func.max(Order.order_number)).where(Order.order_number.like(f"{prefix}%"))
-    )
-    max_num = result.scalar()
-    if max_num:
-        last_seq = int(max_num.split("-")[-1])
-        return f"{prefix}{last_seq + 1:05d}"
-    return f"{prefix}00001"
+# Compat shim — use app.domains.orders.service instead
+from app.domains.orders.service import generate_order_number, check_order_completion
+__all__ = ["generate_order_number", "check_order_completion"]