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/contents/dto/create-content.dto.ts

@@ -6,6 +6,7 @@ import {
 	IsOptional,
 	IsString,
 	IsUUID,
+	MaxLength,
 } from "class-validator";
 
 export enum ContentType {
@@ -19,14 +20,17 @@ export class CreateContentDto {
 
 	@IsString()
 	@IsNotEmpty()
+	@MaxLength(255)
 	title!: string;
 
 	@IsString()
 	@IsNotEmpty()
+	@MaxLength(512)
 	storageKey!: string;
 
 	@IsString()
 	@IsNotEmpty()
+	@MaxLength(128)
 	mimeType!: string;
 
 	@IsInt()
@@ -39,5 +43,6 @@ export class CreateContentDto {
 	@IsOptional()
 	@IsArray()
 	@IsString({ each: true })
+	@MaxLength(64, { each: true })
 	tags?: string[];
 }