feat: create issue #11 - Data Validation

ISSUE-11.md

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+## Issue #11: Implement Data Validation
+
+### Description
+
+Implement comprehensive data validation for all API inputs to ensure data integrity and prevent security vulnerabilities.
+
+### Acceptance Criteria
+
+- [ ] Create validation middleware
+- [ ] Define validation rules for all endpoints
+- [ ] Add error handling for validation failures
+- [ ] Integrate validation with existing routes
+- [ ] Document validation rules
+
+### Tasks
+
+- [ ] Install and configure Joi or express-validator
+- [ ] Create validation middleware
+- [ ] Define validation schemas for API endpoints
+- [ ] Apply validation to all routes
+- [ ] Add comprehensive error messages for validation failures
+
+### Notes
+
+This issue addresses the need for robust data validation to ensure data integrity and prevent security vulnerabilities. The implementation will use a validation library to define rules for all API inputs, with proper error handling and clear error messages for validation failures.