content: update six GSC-priority gateway guides

[Yilialinn]

Summary

• replace absolute cloud/open-source/commercial gateway claims with a neutral evaluation framework
• clarify when microservices and webhook systems use a gateway and which responsibilities remain in services or delivery workers
• update OIDC, gRPC transcoding, and ADC examples to current supported fields and commands
• align English titles and descriptions with demonstrated search intent without changing URLs or canonicals

GSC rationale

The review uses finalized GSC Query+Page data through 2026-08-22. The microservices and webhook articles are the primary pages for their selected queries. Where documentation or another page has stronger ownership (OIDC, gRPC, and the open-source comparison topic), these edits correct unsafe/outdated facts and distinguish the blog intent rather than attempting to replace the primary page. ADC has current first-page visibility but contained obsolete CLI commands, so the rewrite protects the query while restoring technical accuracy.

Validation

• yarn lint:frontmatter
• git diff --check
• NODE_OPTIONS=--max-old-space-size=3072 yarn build:blog:en:preview
• desktop and 390 px mobile checks for all six pages: one H1, matching Title/Meta/canonical, no page-level horizontal overflow
• independent technical/SEO review completed with no remaining P0-P2

The blog-only preview build exits successfully. It reports the repository's existing cross-surface links (for example /docs/ and /learning-center/) because those surfaces are not part of the standalone blog build.