Docs: Update Nebula Integration Guide and Navigation - #1260

Purpose of the change

This PR standardizes the NebulaGraph Enterprise Integration Guide within the MemMachine ecosystem. It ensures the documentation is discoverable via the global navigation and adheres to our Mintlify-native metadata standards.

Description

We are bringing the NebulaGraph Enterprise guide into the official documentation fold. This change addresses the lack of a structured entry point for enterprise graph users.
Key modifications include:

• Navigation Integration: Added the NebulaGraph guide to docs.json for proper sidebar placement.
• Metadata Standardization: Updated the MDX header with specific title, sidebarTitle, icon, and description fields to ensure visual consistency and SEO optimization across the site.
• UI/UX Alignment: Assigned the atom icon to the guide to visually represent the vector graph structure.

Fixes/Closes

Fixes #1225

Type of change

• New feature (non-breaking change which adds functionality)
• Documentation update
• Refactor (does not change functionality, e.g., code style improvements, linting)

How Has This Been Tested?

I have performed manual verification of the documentation structure and metadata.

• Manual verification (list step-by-step instructions)

Test Steps:

1. Validated docs.json syntax to ensure no breaking changes to the navigation tree.
2. Verified MDX frontmatter against Mintlify requirements for title and icon rendering.
3. Confirmed relative pathing and internal references match the current repository structure.

Test Results: Documentation build simulated locally; metadata renders correctly in the sidebar and header.

Checklist

• I have signed the commit(s) within this pull request
• My code follows the style guidelines of this project (See STYLE_GUIDE.md)
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have checked my code and corrected any misspellings

Maintainer Checklist

• Confirmed all checks passed
• Contributor has signed the commit(s)
• Reviewed the code
• Run, Tested, and Verified the change(s) work as expected

Screenshots/Gifs

Screenshot shown new Top of page and entry in left-hand menu:

Further comments

This is the first phase of the NebulaGraph documentation alignment. Future PRs will focus on refactoring the body content to use <Steps> and <Tabs> components to further improve readability.