fix(seo): align Ingress FAQ sitemap and Chinese listing redirects

[Yilialinn]

Task

Classify Remaining Indexing Residuals (P1).

Problem

• The current Ingress FAQ URL was present in the APISIX sitemap although production permanently redirects it to the Ingress overview.
• The Chinese Learning Center listing was present in the Chinese sitemap, but Apache's DirectoryIndex request for index.html matched the retired-article redirect and sent visitors to the English listing.

Changes

• Exclude current Ingress FAQ aliases from both generated sitemaps while retaining their 301 to the current overview.
• Exempt the Chinese listing index.html from the retired article redirect; article slugs still go to their English counterparts.
• Add sitemap and redirect regression tests.

Validation

• npm run test:sitemap; npm run test:redirects; git diff --check.
• Minimal local Apache test: /zh/learning-center/ and /zh/learning-center/index.html return 200; a retired Chinese article route returns 301.
• All 981 URLs in current live sitemaps were compared with redirect rules; the Ingress FAQ was the only directly redirected sitemap URL.
• Full Astro build was not run in this clean worktree because upstream synced docs are absent; CI will validate final generated output.

Post-deploy check

Confirm both FAQ aliases are absent from sitemaps, the Chinese listing returns 200, and retired article URLs remain 301.

No canonical ownership change, including the existing API7 plugin documentation strategy.