docs: rewrite the agent guards landing page

[davidmytton]

Rewrites /guards as an introduction for a new reader, matching the structure of the /coding-agents landing page from #977 and #979.

The page now covers what agent guards are for (actions with no HTTP request, checked with guard() rather than protect()), the key capabilities, use cases mapped to the worked policies in Policy examples, how it works (labels and typed inputs, detectors, Guard policies in Rego, starting points, dry run then live), a guard() versus protect() comparison, a supported-SDKs table with each SDK's framework integrations, the main limitations, and cards to every guide.

No reference material moved: nothing links to an anchor on /guards, and the old page's content already lives on the sub-pages it now links to. The "Observe, enforce, audit" table and the "Where enforcement runs" section are folded into the capabilities and how-it-works sections.

Screenshots for the page were regenerated.

  

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Project	Deployment	Actions	Updated
arcjet-docs	Ready	Preview	Oct 9, 2026 8:08pm UTC

[arcjet-review]

Arcjet Review — 🟢 Low Risk

Decision: Approved

Rationale: Documentation-only change: rewrites a single landing page MDX file and updates two screenshot baselines. No code paths, dependencies, auth, or infrastructure touched. Security review checklist is not applicable to prose. The copy accurately describes concepts referenced elsewhere in the docs (guard() vs protect(), labels, inputs, dry run), and all internal links point to existing documented sections. No secrets, no injection surface, no behavior change.

Summary of Changes

Rewrites /guards as a new-reader-oriented landing page: adds Capabilities, Use cases (table linking to policy examples), How it works (with labels/inputs, detectors, policies, starting points, dry run), a guard() vs protect() comparison, a Supported SDKs table, Limitations, and a refreshed CardGrid. Regenerates the two guards page screenshot baselines.

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