feat(frontend) : add TaskDocument DTO, service and i18n translations

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/services/dto/task.ts

@@ -5,6 +5,7 @@ import type { TaskTag } from './task-tag'
 import type { TaskGroup } from './task-group'
 import type { UserData } from './user-data'
 import type { Project } from './project'
+import type { TaskDocument } from './task-document'
 
 export type Task = {
     id: number
@@ -19,6 +20,7 @@ export type Task = {
     group: TaskGroup | null
     project: Project | null
     tags: TaskTag[]
+    documents: TaskDocument[]
     archived: boolean
 }