migrate 392 questions to pattern format

backend/data/questions/partition-to-k-equal-sum-subsets.yaml

@@ -8,7 +8,8 @@ categories:
   - dynamic-programming
   - recursion
 patterns:
-  - backtracking
+  - slug: backtracking
+    is_optimal: true
 
 function_signature: "def can_partition_k_subsets(nums: list[int], k: int) -> bool:"