migrate 392 questions to pattern format

backend/data/questions/course-schedule.yaml

@@ -6,8 +6,10 @@ leetcode_url: https://leetcode.com/problems/course-schedule/
 categories:
   - graphs
 patterns:
-  - dfs
-  - bfs
+  - slug: dfs
+    is_optimal: false
+  - slug: bfs
+    is_optimal: true
 
 function_signature: "def can_finish(num_courses: int, prerequisites: list[list[int]]) -> bool:"