style: 按 Oxfmt 重新格式化

换格式化器带来的差异，只有 5 个文件：长联合类型改成每项一行、以 | 开头。
和上一个提交分开，方便 blame 时跳过（git blame --ignore-rev）。

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/web/src/oj/learn/composables/useExerciseParse.ts

@@ -1,7 +1,8 @@
 import type { Exercise } from "utils/types"
 
 export type Segment =
-  { type: "md"; content: string } | { type: "exercise"; exercise: Exercise }
+  | { type: "md"; content: string }
+  | { type: "exercise"; exercise: Exercise }
 
 export function parseExercises(
   content: string,