Add backend service for Zen mode tasks

[MaryammAli]

- Description: Add API support for distraction-free coding sessions.
- Path: `BackendAcademy/src/submissions/`

[whitezaddy]

I have experience for this and have reviewed the code; I can submit a PR within 24hrs.

[jesutobaadedejidev]

I would like to work on this issue. Do assign it to me.

[mac-dubem]

I'd like to work on this. I'll implement the API support for distraction-free coding sessions in BackendAcademy/src/submissions/, following the existing architecture and ensuring clean, well-tested integration.

[gloskull]

Hello, I have 4 years of experience delivering solutions for projects like this, covering backend, frontend, and smart contract development. After carefully reviewing your requirements, I have a clear understanding of the task and am confident in my ability to deliver a clean, efficient, and thoroughly tested solution on time. I prioritize code quality, maintainability, and industry best practices throughout the development process. My PR will be submitted in under 10hours.