fix(CopyButton): 修复 review 反馈并补充测试 (#66)

* fix: remove non-functional animation classes from CopyButton
* test(CopyButton): 补充单元测试覆盖边界场景
* fix: unify CopyButton imports to named export across all consumers
* fix(CopyButton): add aria-label for screen reader accessibility

src/pages/Timestamp/LiveClock.tsx

@@ -1,7 +1,7 @@
 import React, { useEffect, useState } from 'react';
 import { Clock } from 'lucide-react';
 import { toast } from 'sonner';
-import CopyButton from '@/components/CopyButton';
+import { CopyButton } from '@/components/CopyButton';
 import type { UnitType } from './constants';
 import { msToUnit } from './constants';
 import { useI18n } from '@/utils/chromeI18n';

src/pages/Timestamp/ResultView.tsx

@@ -1,5 +1,5 @@
 import React from 'react';
-import CopyButton from '@/components/CopyButton';
+import { CopyButton } from '@/components/CopyButton';
 import { useI18n } from '@/utils/chromeI18n';
 import { cn } from '@/lib/utils';