Split server into router/controllers

[fuzziecoder]

Title

refactor: modularize backend into router, controller, and service layers
 
Body
backend/server.js mixes routing and business logic, making maintenance difficult. Refactor into clear modules.
 
Acceptance Criteria

• server.js only handles bootstrapping and middleware.
• Route handlers are separated by feature domain.
• No behavior regressions in existing endpoints.
   

[AnushSingla]

hey @fuzziecoder please assign this to me

[fuzziecoder]

I'm currently working on this issue @AnushSingla here are more other 15+ issues if you're interested in working on any issues please let me know I will assign you