fix: add NEXT_PUBLIC_ to env

[Dun-sin]

Fixes Issue

My PR closes #601

👨‍💻 Changes proposed (What did you do ?)

• add the NEXT_PUBLIC_ for Next.js
• changes Next.js dev command to turn on debugging by default
• installed cross-env for debugging

✔️ Check List (Check all the applicable boxes)

• [x] My code follows the code style of this project.
• [x] This PR does not contain plagiarized content.
• [x] The title and description of the PR is clear and explains the approach.

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[Dun-sin]

@mathiasayivor pls review asap