FEATURE REQUEST:Add request/response schema validation for all backend endpoints using Zod or a similar runtime validator.

### Is your feature request related to a problem?

- [x] Yes, it is related to a problem

### Describe the feature you'd like

## 🌟 Feature Description

Introduce strict **runtime request and response schema validation** for all backend endpoints using **Zod** (or a similar validation library).
Each API route should explicitly define:

* an input schema for request validation
* an output schema for response validation

This ensures that all data entering and leaving the system follows a well-defined contract.

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## 🔍 Problem Statement

Currently, backend endpoints do not enforce strict runtime validation on incoming requests or outgoing responses.
This allows malformed or unexpected data to propagate into business logic, which can lead to:

* runtime crashes
* inconsistent API behavior
* difficult debugging
* potential security vulnerabilities

Additionally, the absence of explicit API contracts makes long-term maintenance and collaboration harder as the codebase grows.

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## 🎯 Expected Outcome

After implementing this feature:

* Every major backend endpoint has:

* validated request payloads
* validated response payloads
* Invalid input is rejected early with clear, consistent error messages
* API behavior becomes more predictable and reliable
* The backend becomes safer, easier to debug, and easier for new contributors to understand

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## 📷 Screenshots and Design Ideas

No UI changes required.

Design concept:

* Introduce a centralized validation middleware layer
* Define schemas alongside route handlers
* Apply validation before request handling and before sending responses

Example approach:

* Use **Zod** schemas for each route
* Integrate schema checking into existing backend routing flow

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## 📋 Additional Context

This enhancement significantly improves:

* system reliability
* API safety
* developer experience
* long-term maintainability

It also lays the foundation for future tooling such as automatic API documentation generation and stronger testing practices.

### Record

- [x] I agree to follow this project's Code of Conduct
- [x] I want to work on implementing this feature