fix(pages): 修复 TypeScript 错误、硬编码字符串，移除死代码

- 修复 LiveClock.tsx CopyButton size 属性类型错误 (small → sm)
- 修复 ToolCard.tsx 紫色 RGB 值拼写错误 (147,51,2 purple → 147,51,232)
- 替换 4 处硬编码中文为 i18n 调用 (StorageCleaner, JsonTools)
- MarkdownToHtml 预览链接色改为 CSS 变量以支持暗黑模式
- 移除 Base64Converter 中已被 Base64ConverterSection 替代的死代码
  (FileMode.tsx, ImageMode.tsx 及其测试文件)
- 更新 README.md 移除对已删除文件的引用

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

i18n/locales/en/jsonDiff.json

@@ -15,6 +15,7 @@
   "diffCount": "{{count}} differences",
   "invalidJson": "Invalid JSON format",
   "emptyHint": "Enter JSON on both sides and click Compare",
+  "fixErrorHint": "Fix the JSON syntax errors above to enable live comparison",
   "added": "Added",
   "removed": "Removed",
   "modified": "Modified"