fix: conditional assetPrefix for dev mode to fix CSS loading

[lemorage]

Description

When running the app in development mode, Next.js serves assets locally (http://localhost:3000/_next/static/...), but the assetPrefix config in next.config.ts is telling it to fetch them from https://demo.mem0.ai. This will make these requests fail with a 404, and the stylesheets don’t load.

This PR resolves this issue by adding a conditional check to avoid this. Plus, the preload: false is added to fonts, fixing the link preload warning in Next.js.

Fixes #2444

Type of change

Please delete options that are not relevant.

• [X] Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Tested by pnpm run dev, all the assets can be found by Next.js, and the demo website works properly.

https://docs.mem0.ai/examples/mem0-demo#enhancing-the-next-js-application

Checklist:

• [X] My code follows the style guidelines of this project
• [X] I have performed a self-review of my own code
• [X] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [X] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] New and existing unit tests pass locally with my changes
• [ ] Any dependent changes have been merged and published in downstream modules
• [X] I have checked my code and corrected any misspellings

Maintainer Checklist

• [ ] closes #xxxx (Replace xxxx with the GitHub issue number)
• [ ] Made sure Checks passed

[CLAassistant]

All committers have signed the CLA.

[alm0ra]

@lemorage Has that PR been put on hold? Could you please look into it?

[parshvadaftari]

@lemorage Can you fix merge conflicts? Thanks