migrate 392 questions to pattern format

backend/data/questions/append-k-integers-with-minimal-sum.yaml

@@ -8,7 +8,8 @@ categories:
   - math
   - sorting
 patterns:
-  - greedy
+  - slug: greedy
+    is_optimal: true
 
 function_signature: "def min_sum(nums: list[int], k: int) -> int:"