CLAP-56 Fix: completedAt을 finishedAt으로 변경

Author: parkjaehak

src/main/java/clap/server/adapter/inbound/web/dto/task/FindTaskDetailsResponse.java

@@ -9,7 +9,7 @@ public record FindTaskDetailsResponse(
         Long taskId,
         String taskCode,
         LocalDateTime requestedAt,
-        LocalDateTime completedAt,
+        LocalDateTime finishedAt,
         TaskStatus taskStatus,
         String requesterNickName,
         String requesterImageUrl,

src/main/java/clap/server/adapter/inbound/web/dto/task/FindTaskListResponse.java

@@ -13,6 +13,6 @@ public record FindTaskListResponse(
         String title,
         String processorName,
         TaskStatus taskStatus,
-        LocalDateTime completedAt
+        LocalDateTime finishedAt
 ) {
 }