支持按用户保存播放器与弹幕偏好

在 user 记录上新增播放器音量、弹幕开关、透明度、字号、显示区域、合并偏好、自定义弹幕源以及 dandanplay 应用凭据字段，并提供 PUT /danmaku/settings 局部更新接口，带取值校验。
返回脱敏后的完整渲染配置，绝不回传应用密钥，仅在响应中标记密钥是否已配置。
结果缓存键加入用户 ID 与凭据指纹，避免不同用户或凭据串用缓存；旧版实例级设置仅作为未登录与迁移期的回退。

web/src/utils/withoutVideoFrame.test.ts

@@ -0,0 +1,30 @@
+import { runWithoutGlobalVideoFrame } from './withoutVideoFrame.ts'
+
+function check(name: string, cond: boolean) {
+  if (!cond) throw new Error(`runWithoutGlobalVideoFrame: ${name}`)
+}
+
+const FakeVideoFrame = function VideoFrame() {
+  return undefined
+}
+
+Object.defineProperty(globalThis, 'VideoFrame', {
+  configurable: true,
+  writable: true,
+  value: FakeVideoFrame,
+})
+
+let seenInside = typeof (globalThis as { VideoFrame?: unknown }).VideoFrame
+const result = runWithoutGlobalVideoFrame(() => {
+  seenInside = typeof (globalThis as { VideoFrame?: unknown }).VideoFrame
+  return 7
+})
+
+check('hides VideoFrame inside the callback', seenInside === 'undefined')
+check('returns the callback result', result === 7)
+check(
+  'restores VideoFrame afterwards',
+  (globalThis as { VideoFrame?: unknown }).VideoFrame === FakeVideoFrame,
+)
+
+console.log('withoutVideoFrame.test.ts ok')