docs(introduction): refine guide overview

[SoonIter]

Summary

• streamline the introduction guide structure and remove repeated sections
• keep preview/playground examples in a single component-docs section
• sync the same cleanup across zh/en docs and remove unnecessary transition animation content

[Copilot]

Pull request overview

Refines the “Introduction” guide structure to reduce repetition, consolidate preview/playground examples into the component-docs section, and align the cleanup across English and Chinese docs.

Changes:

• Expanded and reorganized the “core features” / overview content (theme/customization, doc DX, and related sections).
• Consolidated and updated plugin-preview / plugin-playground examples (removed older screenshot-based sections).
• Cleaned up several internal links and removed the View Transition animation section.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
website/docs/zh/guide/start/introduction.mdx	Restructures the Chinese introduction guide, adds consolidated DX/theme sections, and updates component-doc examples.
website/docs/en/guide/start/introduction.mdx	Mirrors the same restructuring in English, updates plugin examples, and refreshes internal linking/wording.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.