chore(share buttons): add tips for mouse hover

[githubdudu]

已知问题 Background

1. There are so many shared buttons and some of them are unfamiliar to some users. And there is no further way to know about what are these.

解决方案 Proposal

1. Simple and easy: add tips for these buttons when mouse hovering.

改动收益 Benifit

1. More info on the page and more user-friendly.

具体改动 File-level scope

1. Add title attributes for these button components in ShareButtons.js.

测试确认

• 本地开发环境测试通过
• 生产环境构建测试通过

Below is a gif from production env:

其他考虑 Consideration

Right now I only keep it simple, all the words are lower cases.

1. Do we need more standard name for these icons like LinkedIn, instead of linked; QQ instead of qq, etc?
2. Do we need bilingual support? (both english and chinese)

用户文档（docs/user-guide/）

若本 PR 未 修改 docs/user-guide/、docs/developer/ 中与站长相关的说明，可勾选「不适用」并跳过本节。

• 不适用（无文档改动）
• 已按 维护工作流 自检
• 路径符合 docs/user-guide/ 目录约定
• 已更新 user-guide/README.md（新增/移动文章时）
• 已更新 ARTICLE_INDEX.md（新 slug 或路径变更时）
• 环境变量名与 conf/*.config.js 一致（若文档涉及配置）
• 示例中无真实 Token、.env、私有 ID
• 保留或更新了「原文链接」（若源自 docs.tangly1024.com）

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