Configurable viewport docs

[hiroTamada]

Description

This PR introduces documentation for the new configurable viewport feature, allowing users to set a custom width, height, and refresh_rate for browser sessions.

• Adds a new page, browsers/viewport.mdx, with code examples for TypeScript/JavaScript and Python, a list of supported configurations, and performance considerations.
• Updates docs.json to include the new page in the "Browsers" section of the navigation.
• Updates the info/pricing.mdx page to show that "Browser viewports" are available on all subscription tiers.

Implementation Checklist

• If updating our sample apps, update the info in our Quickstart
• If updating our CLI, update the info in our CLI

Testing

• mintlify dev works (see installation here)

Docs

• Link to a PR in our docs repo documenting your change (if applicable)

Visual Proof

Please provide a screenshot or video demonstrating that your changes work locally:

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Related Issue

Fixes [Github issue link]

[If this corresponds to a fix from another Kernel OSS repo, include this:]

Fixes [Link to other repo]

[Replace with actual issue link, e.g., Fixes https://github.com/username/repo/issues/123]

Additional Notes

[Any additional context, concerns, or notes for reviewers]

^{Description generated by Mesa. Update settings}

[dprevoznik]

Left one comment!

[dprevoznik]

Can we move this directly above Browser Replays in the Pricing features list?

[hiroTamada]

done

[masnwilliams]

lgtm

[dprevoznik]

LGTM now!