feat(dto): enforce field length constraints across DTOs

Add `@MaxLength` validations to limit string field lengths in multiple DTOs, ensuring consistent data validation and integrity. Integrate `CreateApiKeyDto` in the API keys controller for improved type safety.

backend/src/users/dto/update-consent.dto.ts

@@ -1,11 +1,13 @@
-import { IsNotEmpty, IsString } from "class-validator";
+import { IsNotEmpty, IsString, MaxLength } from "class-validator";
 
 export class UpdateConsentDto {
 	@IsString()
 	@IsNotEmpty()
+	@MaxLength(16)
 	termsVersion!: string;
 
 	@IsString()
 	@IsNotEmpty()
+	@MaxLength(16)
 	privacyVersion!: string;
 }