Refactor backend services from monolithic to domain-based modules

[Smartdevs17]

Description

Backend services are in flat files mixing concerns. Refactor to domain-based modules with clear boundaries and dependency injection.

Acceptance Criteria

• Domain modules: subscription, billing, notification, analytics
• Service interfaces with DI container
• Module-level error handling
• Reduced cross-module coupling
• Module-level test coverage
• Documentation of module boundaries

Technical Scope

• backend/services/
• Edge: shared infrastructure (logging, config) across modules, circular dependencies

[Theraxia]

@Theraxia has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

hi maintainer, i would like to work on this

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

[sweetesty]

@sweetesty has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

hi maintainer please ill like to work on this issue

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

[danieloche635-bit]

@danieloche635-bit has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

will love to work on this issue

ℹ️ Repo Maintainers: To accept this application, review their application or assign @danieloche635-bit to this issue.

[drips-wave]

Congratulations, @sweetesty! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 2, 2026.

🧑‍💻 @sweetesty: 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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