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-document.ts

@@ -0,0 +1,13 @@
+import type { UserData } from './user-data'
+
+export type TaskDocument = {
+    '@id'?: string
+    id: number
+    task: string
+    originalName: string
+    fileName: string
+    mimeType: string
+    size: number
+    createdAt: string
+    uploadedBy: UserData | null
+}