fix: deduplicate order_number collisions during Firestore orders migration

backend/migration/migrate_crm_orders.py

@@ -71,6 +71,7 @@ async def run() -> None:
 
     records = []
     skipped = 0
+    seen_order_numbers: set[str] = set()
     for doc in docs:
         d = doc.to_dict()
 
@@ -91,6 +92,12 @@ async def run() -> None:
             continue
 
         order_number = d.get("order_number") or f"ORD-LEGACY-{doc.id}"
+        # Deduplicate: if this order_number was already seen in this batch,
+        # make it unique by appending the doc ID suffix.
+        if order_number in seen_order_numbers:
+            order_number = f"{order_number}-{doc.id[:8]}"
+            print(f"  INFO: duplicate order_number — renamed to {order_number}")
+        seen_order_numbers.add(order_number)
 
         created_at = _coerce_dt(d.get("created_at")) or _now_utc()
         updated_at = _coerce_dt(d.get("updated_at")) or _now_utc()