fix: 兼容 Chrome 90 前端运行环境

- 为管理端与用户中心补齐旧浏览器运行时 API 和回归测试

- 增加现代 CSS 与选择器降级，保持现有界面效果

- 固定 Chrome 90 构建目标并补充兼容依赖

easyflow-ui-admin/app/src/polyfills.test.ts

@@ -0,0 +1,108 @@
+import { afterEach, beforeEach, describe, expect, it } from 'vitest';
+
+import {
+  installArrayAtPolyfill,
+  installObjectHasOwnPolyfill,
+  installPromiseWithResolversPolyfill,
+  installStringAtPolyfill,
+  installStructuredClonePolyfill,
+  installUrlCanParsePolyfill,
+} from './polyfills';
+
+const descriptors = new Map<
+  string,
+  [object, PropertyKey, PropertyDescriptor | undefined]
+>();
+
+function remember(key: string, target: object, property: PropertyKey) {
+  descriptors.set(key, [
+    target,
+    property,
+    Object.getOwnPropertyDescriptor(target, property),
+  ]);
+}
+
+function remove(target: object, property: PropertyKey) {
+  Reflect.deleteProperty(target, property);
+}
+
+beforeEach(() => {
+  remember('arrayAt', Array.prototype, 'at');
+  remember('stringAt', String.prototype, 'at');
+  remember('hasOwn', Object, 'hasOwn');
+  remember('withResolvers', Promise, 'withResolvers');
+  remember('structuredClone', globalThis, 'structuredClone');
+  remember('canParse', URL, 'canParse');
+});
+
+afterEach(() => {
+  for (const [target, property, descriptor] of descriptors.values()) {
+    if (descriptor) Object.defineProperty(target, property, descriptor);
+    else remove(target, property);
+  }
+  descriptors.clear();
+});
+
+describe('chrome 90 browser polyfills', () => {
+  it('installs Array.prototype.at and String.prototype.at', () => {
+    remove(Array.prototype, 'at');
+    remove(String.prototype, 'at');
+
+    installArrayAtPolyfill();
+    installStringAtPolyfill();
+
+    expect(['first', 'last'].at(-1)).toBe('last');
+    expect('EasyFlow'.at(-1)).toBe('w');
+    expect('EasyFlow'.at(99)).toBeUndefined();
+  });
+
+  it('installs Object.hasOwn without accepting inherited properties', () => {
+    remove(Object, 'hasOwn');
+    installObjectHasOwnPolyfill();
+
+    const value = Object.create({ inherited: true }) as { own?: boolean };
+    value.own = true;
+    expect(Object.hasOwn(value, 'own')).toBe(true);
+    expect(Object.hasOwn(value, 'inherited')).toBe(false);
+  });
+
+  it('installs Promise.withResolvers and exposes working callbacks', async () => {
+    remove(Promise, 'withResolvers');
+    installPromiseWithResolversPolyfill();
+
+    // eslint-disable-next-line n/no-unsupported-features/es-syntax -- 测试目标就是验证该 API 的兼容实现。
+    const { promise, resolve } = Promise.withResolvers<string>();
+    resolve('ready');
+    await expect(promise).resolves.toBe('ready');
+  });
+
+  it('installs structuredClone with complex value and cycle support', () => {
+    remove(globalThis, 'structuredClone');
+    installStructuredClonePolyfill();
+
+    const source: {
+      createdAt: Date;
+      lookup: Map<string, number>;
+      self?: unknown;
+    } = {
+      createdAt: new Date('2026-07-15T00:00:00.000Z'),
+      lookup: new Map([['answer', 2026]]),
+    };
+    source.self = source;
+    const clone = structuredClone(source);
+
+    expect(clone).not.toBe(source);
+    expect(clone.self).toBe(clone);
+    expect(clone.createdAt).toEqual(source.createdAt);
+    expect(clone.lookup.get('answer')).toBe(2026);
+  });
+
+  it('installs URL.canParse for absolute and base-relative URLs', () => {
+    remove(URL, 'canParse');
+    installUrlCanParsePolyfill();
+
+    expect(URL.canParse('https://easyflow.example/chat')).toBe(true);
+    expect(URL.canParse('/chat', 'https://easyflow.example')).toBe(true);
+    expect(URL.canParse('/chat')).toBe(false);
+  });
+});