[Docs] Add Backend Architecture Documentation

[Abd-Standard]

Description

Document the architecture of NotifyChain backend services, highlighting responsibilities, communication patterns, and data flow.

Tasks
Document service responsibilities.
Explain API interactions.
Describe storage architecture.
Add architecture diagrams.

Acceptance Criteria
Architecture documentation is complete.
New contributors can understand system design.
Diagrams are included.

Contributors start work by running:
git checkout -b docs/backend-architecture

[shadrach68]

@shadrach68 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I would like to work on this issue because I am a full-stack developer with 5+ years experience. I focus on identifying root causes and delivering clean, efficient, and maintainable solutions, with thorough testing to ensure reliable results.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @shadrach68 to this issue.

[Xoulomon]

@Xoulomon has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hey Maintainer, I have gone through the details of the issue and i am capable of resolving it, I would love to be assigned to work on it ASAP. Thanks in advance

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

[drips-wave]

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

🧑‍💻 @Xoulomon: 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.

Warning

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊

[grantfox-oss]

🦊 GrantFox — @Xoulomon has been assigned to this issue as part of the Official Campaign campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #276)
2. Your PR will be reviewed by the Core-Foundry maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign campaign!

@Xoulomon's PR #321 was approved and merged by @Abd-Standard.

🏆 @Xoulomon: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (156 total points). Track your full progress on GrantFox.

👏 Great work, @Xoulomon! Keep contributing to Core-Foundry.

[drips-wave]

This issue has been completed by @Xoulomon as part of the Stellar Wave Program's 6th Wave 🥳

😎 @Xoulomon: 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.

🧑‍💻 Repo maintainers: How'd the contributor do? Leave a review to share your experience working with them.