docs(web): clarify CDN caching, bump API stale-while-revalidate, and tidy README table

[connortsui20]

Motivation

• Clarify CDN caching semantics for HTML pages and API routes, fix wording/formatting in the environment variable table, and increase the API route stale-while-revalidate window to better preserve low-traffic warmth.

Description

• Reformat the web/README.md environment variable table for consistent column alignment and readability, change API routes Cache-Control stale-while-revalidate from 300 to 3600, and expand explanatory text about Vercel CDN behavior and HTML 404 caching rules.

Testing

• This is a documentation-only change so no functional tests were required and repository CI formatting/lint checks are expected to be unaffected.

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Codex Task

[github-actions]

Vercel preview for 1d3b4f7ab05a79479d242fabbfb09ca1549c57b7: https://benchmarks-website-9plu1ui3k-vortex-data.vercel.app