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/JsonTools/JsonConvertSection.tsx

@@ -1,7 +1,7 @@
 import React, { useEffect, useMemo, useState } from 'react';
 import { useI18n } from '@/utils/chromeI18n';
 import { formatBytes } from '@/utils/format';
-import CopyButton from '@/components/CopyButton';
+import { CopyButton } from '@/components/CopyButton';
 import TextInputArea from '@/components/TextInputArea';
 import { validateJson } from '@/utils/jsonFormatter';
 import { cn } from '@/lib/utils';

src/pages/JsonTools/JsonFormatSection.tsx

@@ -7,7 +7,7 @@ import {
   validateJson,
 } from '@/utils/jsonFormatter';
 import { formatBytes } from '@/utils/format';
-import CopyButton from '@/components/CopyButton';
+import { CopyButton } from '@/components/CopyButton';
 import SwitchButtonGroup from '@/components/SwitchButtonGroup';
 import TextInputArea from '@/components/TextInputArea';
 import { Checkbox } from '@/components/ui/checkbox';