migrate 392 questions to pattern format

backend/data/questions/all-paths-from-source-to-target.yaml

@@ -7,8 +7,10 @@ categories:
   - graphs
   - recursion
 patterns:
-  - dfs
-  - backtracking
+  - slug: dfs
+    is_optimal: true
+  - slug: backtracking
+    is_optimal: false
 
 function_signature: "def all_paths_source_target(graph: list[list[int]]) -> list[list[int]]:"