docs: 调整 Realtime Recipe 标题与适用范围表述

[LibraTang]

Summary

• Content type: Recipe
• Locale: zh-CN / en-US
• Demo source included: no
• Target audience: 接入 QCA Realtime 的应用开发者。
• User problem and expected outcome: 标题改为“为你的应用接入 QCA Realtime”，英文同步改为“Integrate QCA Realtime into Your Application”。摘要同步调整，开头明确浏览器与服务端是本文示例架构，前置条件标为“示例环境”。

Sources and assets

• Public sources used: 延续已合入的 PR #18 及文章中的公开来源；本次仅调整措辞。
• Asset owner and license: 文本按仓库 CC BY 4.0；无新增素材、依赖或 Demo。
• 本次文字调整为原创编辑，原文来源保留。

Specialist review

• Maintainer 内容审核；无 API 或代码行为变更。
• Validation: npm run check 全部通过（68 项测试、12 篇内容校验、链接及预览构建）；git diff --check 通过。

Author checklist

• I used exactly one author and no more than five approved tags.
• The article has at least three ## sections and no hand-written table of contents.
• I did not use GitHub Alerts, video, raw HTML, JavaScript, MDX, iframe, remote images, SVG, or interactive content.
• Images are local PNG, JPEG, or WebP files with meaningful alternative text and documented rights. (N/A: no images.)
• The contribution contains no credentials, customer data, personal information, internal links, or unreleased capabilities.
• If a Demo is included, demos/<slug>/ matches the owner article, and the article contains the exact GitHub Demo link. (N/A.)
• If a Demo is included, its README documents prerequisites, setup, run, verification, cleanup, and cost/safety considerations. (N/A.)
• Demo configuration uses placeholders; no dependency cache, build output, binary, archive, nested Git metadata, or symbolic link is included. (N/A.)
• I disclosed the origin and license of Demo source, dependencies, fixtures, and third-party assets. (No new assets.)
• I reviewed the generated preview locally or from the required GitHub Actions checks.
• Every commit contains a Signed-off-by trailer.
• I understand that maintainer Merge to main is the publication event.

Maintainer Demo review

No Demo is included.

• Not applicable, or a Maintainer reviewed the Demo README and source manually.
• Not applicable, or the claimed result, cleanup, billable operations, permissions, and destructive side effects were reviewed.