docs: add a Tooling section for utilities that work with AGENTS.md

[zackabrah]

Disclosure: I'm the author of Scopeglass.

The site lists agents that consume the AGENTS.md format, but no supporting
tooling yet. This adds a small "Tooling" section (matching the AboutSection
component style) with one entry:

• Scopeglass — local CLI that
  shows the effective AGENTS.md chain for any path: precedence order,
  line-level provenance, context-size estimates, and checks for broken
  references, duplicates, and conflicting guidance. Includes a CI gate
  (scopeglass check).

No network calls, no model calls, MIT. Happy to trim this to a single FAQ
line instead if a dedicated section feels premature.

npx tsc --noEmit passes. pnpm-lock.yaml untouched.

[vercel]

@junklabgames-droid is attempting to deploy a commit to the openai Team on Vercel.

A member of the Team first needs to authorize it.