feat(validation): add input validation coverage

[shamoo53]

Input Validation Coverage

Overview

This PR improves overall input validation consistency across the backend by ensuring all request payloads are properly validated using class-validator and NestJS validation pipes.

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Background

Several endpoints were found to lack proper DTO-level validation, increasing the risk of invalid or unexpected data reaching the service layer. This update enforces strict validation rules across all modules.

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Changes Introduced

• Audited all existing DTOs across modules
• Added missing class-validator decorators where required
• Standardized validation rules across all request payloads
• Enabled global ValidationPipe in main.ts to enforce runtime validation
• Ensured transformation and whitelist behavior for incoming requests

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Updated Files

• src/modules/**/dto/*.ts — Added validation decorators and improved DTO definitions
• src/main.ts — Added global ValidationPipe configuration

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Labels

backend, validation, priority-high, security

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Acceptance Criteria

• All incoming requests are validated using DTO rules
• Invalid payloads are rejected with proper error responses
• No unvalidated inputs reach service layer
• Global validation pipe is active across all endpoints
  Closes Input Validation Coverage #259

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[RUKAYAT-CODER]

kindly resolve conflict