docs: add Browser Sandbox page to navigation

[LegoGuy32109]

Summary

Adds the existing features/browser page to the base English navigation beside features/interact. The page is live, but the missing entry keeps Browser Sandbox out of the sidebar, sitemap.xml, and llms.txt.

Validation

• Parsed docs.json with Python.
• Passed git diff --check.
• Confirmed /features/browser returns 200 but is absent from the current sitemap.xml and llms.txt.

Scope

This change adds one line to docs.json. Localized navigation entries and existing redirects remain unchanged.

[hmishra2250]

Heads up: #1364 and #1369 are now stacked on top of this PR, since all three edit docs.json around the same navigation lines.

#1364 resolves the features/browser placement by grouping it with features/interact under an "Interact / Browser Sandbox" group, so the page appears exactly once in the nav. #1369 then stacks on #1364.

Nothing here needs to change. This PR stays targeted at main and merges first. After it lands, the other two get retargeted to main.

• Scope the capabilities page and add Cloud availability per row #1364
• Fix interact sample variables, dead paths, and crawler access guidance #1369

[hmishra2250]

Merging this now as the base of the AX docs stack — several follow-up PRs (capabilities page, inbound links, sample fixes) are branched on top of it. Thanks for catching that the Browser Sandbox page was missing from the nav, @LegoGuy32109.