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/categories/dto/create-category.dto.ts

@@ -1,15 +1,18 @@
-import { IsNotEmpty, IsOptional, IsString } from "class-validator";
+import { IsNotEmpty, IsOptional, IsString, MaxLength } from "class-validator";
 
 export class CreateCategoryDto {
 	@IsString()
 	@IsNotEmpty()
+	@MaxLength(64)
 	name!: string;
 
 	@IsOptional()
 	@IsString()
+	@MaxLength(255)
 	description?: string;
 
 	@IsOptional()
 	@IsString()
+	@MaxLength(512)
 	iconUrl?: string;
 }