fix: detect Next.js environment and adjust the AOI preset file paths

[dzole0311]

Related Ticket: #1259
Related Next.js PR for testing: NASA-IMPACT/next-veda-ui#23

Description of Changes

• Added new isNextJs() util function to detect Next.js environments
• Adjust the AOI preset path to use the new util for setting the correct path to the assets
• Persist backwards compatibility for legacy instances that require the /public/ path prefix
• Removed redundant comments

Notes & Questions About Changes

{Add additonal notes and outstanding questions here related to changes in this pull request}

Validation / Testing

Please test in both repositories:

veda-ui:

1. Using the preview deployment, check that preset AOIs load correctly when selecting different states
2. Test locally to confirm the same functionality
3. Optional: Check in a legacy instance (e.g. GHG Center) that AOIs still load with the /public/ prefix

In next-veda-ui:

1. Using the preview deployment, check that preset AOIs load correctly when selecting different states
2. Test locally to confirm the same functionality works

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[AliceR]

Thanks for adding comments, and cleaning up as well! 🧹

[dzole0311]

Closing this PR since we decided to fix it by creating a /public subdirectory within the /public directory on the Next.js instance side.