[Backend] Create server CONTRIBUTING.md

[Yunusabdul38]

Description: Facilitate easier onboarding for backend developers by creating a dedicated contribution guide for the server project. Tasks:

Create server/CONTRIBUTING.md.
Document environment setup, database migrations, and testing requirements.
Include standard commands for development.

[Rajkoli145]

@Rajkoli145 has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

Hi ,
I’d like to work on this issue.

I’ll create a clear and structured CONTRIBUTING.md for the backend, covering setup steps, contribution workflow, and basic guidelines to help new contributors get started smoothly.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Rajkoli145 to this issue.

[SamixYasuke]

@SamixYasuke has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

Hi maintainer, I have experience documenting codebases and I'd like to handle this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @SamixYasuke to this issue.

[Sundriveauto]

@Sundriveauto has applied to work on this issue as part of the Stellar Wave Program's 3rd wave.

pls i will love to work on this issues

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Sundriveauto to this issue.

[drips-wave]

Congratulations, @Sundriveauto! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on March 30, 2026.

🧑‍💻 @Sundriveauto: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

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[drips-wave]

This issue has been completed by @Sundriveauto as part of the Stellar Wave Program's 3rd Wave 🥳

😎 @Sundriveauto: You earned 200 Points for completing this issue! After the current Wave ends, you'll be eligible for a percentage of the Wave's reward pool based on the percentage of total points you've earned. Learn more here. You can also Leave a review to share your experience working on this issue.

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