feat(security): add security hardening — Helmet, CORS, rate limiting, input sanitization

- Add Helmet with CSP, HSTS, referrer policy
- Configure CORS with environment-based origins
- Add global validation pipe with whitelist mode
- Add SanitizeInputMiddleware for XSS prevention
- Add ThrottlerBehindProxyGuard for rate limiting
- Add FileValidationPipe for upload security
- Set request body size limit to 1MB

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/api/src/modules/shared/infrastructure/index.ts

@@ -5,4 +5,8 @@ export { EventBusService } from './event-bus.service';
 export { GlobalExceptionFilter } from './filters/global-exception.filter';
 export { CorrelationIdMiddleware } from './middleware/correlation-id.middleware';
 export { RequestLoggingMiddleware } from './middleware/request-logging.middleware';
+export { SanitizeInputMiddleware } from './middleware/sanitize-input.middleware';
 export { maskPii } from './pii-masker';
+export { ThrottlerBehindProxyGuard } from './guards/throttler-behind-proxy.guard';
+export { FileValidationPipe } from './pipes/file-validation.pipe';
+export type { FileValidationOptions } from './pipes/file-validation.pipe';