docs: add GPUI design and coding guides (#2801)

## Description

Add canonical English and Chinese Design Guides and Coding Guides for
GPUI Component. The guides capture the project’s desktop interaction
conventions, hierarchy, alignment, theme and rem usage, interface
language, component boundaries, naming, state ownership, and
feature-crate architecture.

This also adds theme-adaptive architecture and alignment diagrams,
places the guides after Getting Started in the sidebar and in the
footer, normalizes related Chinese documentation titles and punctuation,
and links the root AI guidance to the canonical guides.

## Screenshot

The new guide pages include light/dark SVG diagrams for application
architecture and alignment-spine review.

## How to Test

- Run: cd website && node ./node_modules/vitepress/bin/vitepress.js
build
- Validate the four SVG assets with xmllint --noout.
- Open both locales and confirm the sidebar order is Getting Started,
Design Guides, Coding Guides.
- Switch the site theme and confirm both diagrams select the correct
light/dark asset.

## Checklist

- [x] I have read the CONTRIBUTING document and followed the guidelines.
- [x] Reviewed the changes in this PR and confirmed AI-generated content
is accurate.
- [ ] Passed cargo run for story tests related to the changes
(documentation-only change; not applicable).
- [ ] Tested macOS, Windows and Linux platform performance
(documentation-only change; not applicable).