Add instant previews page

[mintlify]

Summary

• Added new page explaining the instant previews feature (URL swap from github.com to mintlify.com)
• Documents the generation process: provisioning, analysis, generation, review, deployment
• Explains how content is kept updated by tracking source repository and commit SHA
• Added to Get started navigation group

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Note

Low Risk
Low risk documentation-only change that updates site navigation and adds a new MDX page with no runtime logic changes.

Overview
Documents the Instant previews feature in a new instant-previews.mdx page, including the URL swap flow, generation steps, update behavior, requirements, and how to claim a generated site.

Updates docs.json to surface the new page under the Get started navigation group.

^{Written by Cursor Bugbot for commit 0ef6352. This will update automatically on new commits. Configure here.}