feat: setup global request validation and payment DTOs

[Wisdom2788]

Closes #3

Overview

Implements global request validation for Stellar Pay using NestJS ValidationPipe. This ensures all incoming payloads are strictly validated, sanitized, and transformed into DTO instances before reaching the controllers.

Changes

• Global Validation: Configured ValidationPipe in main.ts with whitelist, forbidNonWhitelisted, and transform enabled.
• DTO Implementation: Created CreatePaymentIntentDto with:
  • amount: Numeric, minimum 0.01.
  • currency: Strict Enum validation.
  • metadata: Optional object validation.
• Dependencies: Added class-validator and class-transformer.

Checklist

• Enable ValidationPipe in main.ts
• Strip non-whitelisted properties
• Throw error on unknown properties
• Enable auto-transformation to DTO classes
• Implement CreatePaymentIntentDto

How to Test

1. Run pnpm install to get the new validation packages.
2. Start the app: pnpm run start:dev.
3. Test Validation: Send a POST with an amount < 0.01 or an invalid currency; verify a 400 Bad Request response.
4. Test Strictness: Send a request with an extra field (e.g., unknown: true); verify it is rejected.

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[MissBlue00]

@Wisdom2788 ci/cd checks failed, please resolve

[Wisdom2788]

ci/cd checks passed, i await your approval.