feat: migrate AntV site to Astro platform

[lxfu1]

Summary

• migrate the AntV website from the legacy dumi runtime to Astro and the shared @antv/site integration
• add the redesigned bilingual homepage, responsive 1440px content layouts, shared QA entry/result flow, product content, and visual assets
• register the Astro docs content collection and add the missing English document frontmatter
• update package scripts, TypeScript configuration, documentation, CI, and deployment for Node 22 and pnpm 10
• preserve the custom domain through public/CNAME

Platform dependency

CI and deployment pin antvis/site at 8da268521d695766fdf6e5b54d8142cfc19a0032. Repository variables can override the platform repository or revision when needed.

Review fixes

• corrected the platform checkout from the nonexistent antvis/site-platform default to antvis/site
• build the linked platform before checking or building the consumer
• removed calls to the deleted consumer verify script
• made the checkout token fall back to github.token for public/fork PR validation
• moved CNAME into Astro's tracked public directory
• removed the temporary homepage design notes and internal image references from the PR history

Validation

• astro check: 4 files, 0 errors, 0 warnings, 0 hints
• CI and deploy workflow YAML parsing passed
• git diff --check passed
• local browser checks passed for the homepage responsive breakpoints and the Result page new-conversation/history flow, including a 375px viewport

A full production build and full test suite were not run locally per repository validation policy. The PR workflow runs the consumer check and production build against the pinned platform revision.

Known risk

The new homepage visual assets total about 6.9 MB, including a roughly 2.8 MB hero GIF. They are retained to preserve the approved visual design; asset-format optimization can be handled separately with visual QA.