feat(test-case): 测试耗时自动计算（逻辑同开发任务）

- TestCase 新增 startedAt / completedAt 字段
- 流转到"执行中"时记录 startedAt
- 流转到"通过/失败/阻塞"时记录 completedAt
- 回退到执行中时清除 completedAt
- 测试耗时 = startedAt → completedAt 工作日 × 8h
- 列表行显示耗时，详情抽屉显示开始/完成/耗时

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/stores/useTestCaseStore.ts

@@ -76,12 +76,17 @@ export const useTestCaseStore = create<TestCaseState>((set, get) => ({
     }
     const today = new Date().toISOString().slice(0, 10);
     const patch: Partial<TestCase> = { status: to };
+    // 开始执行时间
+    if (to === 'running' && !tc.startedAt) patch.startedAt = today;
+    // 执行完成时间（通过/失败/阻塞都算执行完成）
+    if (to === 'passed' || to === 'failed' || to === 'blocked') patch.completedAt = today;
     if (to === 'running' || to === 'passed' || to === 'failed' || to === 'blocked') {
       patch.executedAt = today;
     }
+    // 回退到执行中时清除完成时间
+    if (to === 'running') { patch.failReason = undefined; patch.blockReason = undefined; patch.completedAt = undefined; }
     if (to === 'failed' && extra?.failReason) patch.failReason = extra.failReason;
     if (to === 'blocked' && extra?.blockReason) patch.blockReason = extra.blockReason;
-    if (to === 'running') { patch.failReason = undefined; patch.blockReason = undefined; }
     get().updateTestCase(id, patch);
     return { ok: true };
   },