chore: 加 oxlint，现存 19 条 warning 清零

原来只有 Prettier，没有任何 lint。根目录加 `bun run lint`（oxlint，覆盖后端、前端、
契约，--deny-warnings：有一条就算失败），CLAUDE.md 常用检查里加上。

现存 19 条顺手清掉：
- 11 处未使用的 import / catch 参数 / 回调参数
- oj/store/problem.ts：`...problem.value?.languages` 展开可能是 undefined
  （外层 if 已经保证非空，去掉 ?.）
- admin/problem/detail.vue：`contestId = contestId` 自赋值，删掉
- judge/sql/engine.ts：注释里的 `/*x*/` 示例原来靠零宽空格防止提前闭合注释，
  改成 `*\/`
- 其余：多余的 !!、new Array(n)、展开里多余的 `|| {}`

两边类型检查、前端构建、后端单二进制编译都过。

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

apps/web/src/oj/contest/components/LineChart.vue

@@ -113,7 +113,7 @@ const chartData = computed(() => {
       if (b.solved !== a.solved) return b.solved - a.solved
       return a.penalty - b.penalty
     })
-    const ranks = new Array(topUsers.length).fill(0)
+    const ranks = Array.from({ length: topUsers.length }, () => 0)
     indexed.forEach((item, pos) => {
       ranks[item.i] = pos + 1
     })

apps/web/src/oj/problem/components/EditorForTest.vue

@@ -12,7 +12,7 @@ import { copyToClipboard } from "utils/functions"
 
 const message = useMessage()
 const route = useRoute()
-const contestID = !!route.params.contestID ? route.params.contestID : null
+const contestID = route.params.contestID ? route.params.contestID : null
 
 const codeStore = useCodeStore()
 const problemStore = useProblemStore()

apps/web/src/oj/store/contest.ts

@@ -106,7 +106,7 @@ export const useContestStore = defineStore("contest", () => {
   async function _getProblems(contestID: string) {
     try {
       problems.value = await getContestProblems(contestID)
-    } catch (err) {
+    } catch {
       problems.value = []
       toggleAccess(false)
     }

apps/web/src/oj/store/problem.ts

@@ -29,7 +29,7 @@ export const useProblemStore = defineStore("problem", () => {
 
   const languages = computed<LANGUAGE[]>(() => {
     if (route.name === "problem" && problem.value?.allowFlowchart) {
-      return ["Flowchart", ...problem.value?.languages]
+      return ["Flowchart", ...problem.value.languages]
     }
     return problem.value?.languages ?? []
   })