Add onboarding status as a subpage to platform domain

[amrit110]

This pull request introduces comprehensive developer documentation and updates the onboarding dashboard deployment to support path-based routing via Google Cloud Load Balancer. It also improves the onboarding dashboard’s Next.js configuration and fetch logic to ensure correct API routing. The navigation structure in mkdocs.yml is reorganized to better separate developer and CLI documentation.

Documentation and Infrastructure Improvements:

• Added a new docs/developer_guide.md covering platform architecture, deployment, administration, and maintenance procedures for the AI Engineering Platform.
• Added a detailed step-by-step setup guide for serving the onboarding dashboard via path-based routing on the load balancer in docs/onboarding-status-web-load-balancer-setup.md.
• Updated mkdocs.yml navigation to group developer documentation and CLI reference, and removed the obsolete user guide. [1] [2]

Onboarding Dashboard Configuration:

• Configured Next.js with basePath: '/onboarding' in services/onboarding-status-web/next.config.js to support serving the app under a subpath.
• Updated the API fetch path in services/onboarding-status-web/app/page.tsx to use /onboarding/api/participants, ensuring requests are routed correctly through the load balancer.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.96%. Comparing base (c96d727) to head (0b138b2).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #31   +/-   ##
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  Coverage   87.96%   87.96%           
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  Files           3        3           
  Lines         457      457           
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  Hits          402      402           
  Misses         55       55           

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