migrate 392 questions to pattern format

backend/data/questions/reverse-string.yaml

@@ -7,7 +7,8 @@ categories:
   - strings
   - two-pointers
 patterns:
-  - two-pointers
+  - slug: two-pointers
+    is_optimal: true
 
 function_signature: "def reverse_string(s: list[str]) -> None:"