fix: improve production docs hub navigation

[Yilialinn]

Changes:

• update the production Astro docs hub description for API Gateway, AI Gateway, Ingress Controller, Helm, plugin development, tutorials, and API references
• add task-based links for getting started, Kubernetes, Helm, and the Java, Go, and Python plugin runners
• clarify that version selectors are available only for supported documentation sets
• keep the existing Documentation / 文档 title and H1 unchanged

Why:

PR #2113 updated the legacy Docusaurus docs landing page, but deployment overlays /docs/ and /zh/docs/ with the Astro output. This follow-up applies the intended navigation and on-page guidance to the source that actually reaches production. It does not claim that each project card opens the latest software release.

Validation:

• verified the Astro production overlay path in .github/workflows/deploy.yml
• verified all 12 English and Chinese task-link targets are reachable
• verified English and Chinese copy, nav labels, responsive wrapping, and focus-visible behavior
• git diff --check
• independent review: P0-P3 = 0
• full Astro build not run locally because available disk space is below the repository workstation safety threshold; remote CI should perform the complete build

Screenshots of the change:

Not included; this is a focused static docs-hub copy and navigation correction.