feat : add task management with kanban and backlog

Add kanban board with drag-and-drop, backlog section, task/group
drawers, DTOs, services, and i18n translations.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/services/dto/task-effort.ts

@@ -0,0 +1,9 @@
+export type TaskEffort = {
+    id: number
+    '@id'?: string
+    label: string
+}
+
+export type TaskEffortWrite = {
+    label: string
+}

frontend/services/dto/task-group.ts

@@ -0,0 +1,17 @@
+import type { Project } from './project'
+
+export type TaskGroup = {
+    id: number
+    '@id'?: string
+    title: string
+    description: string | null
+    color: string
+    project: Project | null
+}
+
+export type TaskGroupWrite = {
+    title: string
+    description: string | null
+    color: string
+    project: string
+}

frontend/services/dto/task-priority.ts

@@ -0,0 +1,11 @@
+export type TaskPriority = {
+    id: number
+    '@id'?: string
+    label: string
+    color: string
+}
+
+export type TaskPriorityWrite = {
+    label: string
+    color: string
+}

frontend/services/dto/task-status.ts

@@ -0,0 +1,13 @@
+export type TaskStatus = {
+    id: number
+    '@id'?: string
+    label: string
+    color: string
+    position: number
+}
+
+export type TaskStatusWrite = {
+    label: string
+    color: string
+    position: number
+}

frontend/services/dto/task-type.ts

@@ -0,0 +1,11 @@
+export type TaskType = {
+    id: number
+    '@id'?: string
+    label: string
+    color: string
+}
+
+export type TaskTypeWrite = {
+    label: string
+    color: string
+}

frontend/services/dto/task.ts

@@ -0,0 +1,31 @@
+import type { TaskStatus } from './task-status'
+import type { TaskEffort } from './task-effort'
+import type { TaskPriority } from './task-priority'
+import type { TaskType } from './task-type'
+import type { TaskGroup } from './task-group'
+import type { UserData } from './user-data'
+
+export type Task = {
+    id: number
+    '@id'?: string
+    title: string
+    description: string | null
+    status: TaskStatus | null
+    effort: TaskEffort | null
+    priority: TaskPriority | null
+    assignee: UserData | null
+    group: TaskGroup | null
+    types: TaskType[]
+}
+
+export type TaskWrite = {
+    title: string
+    description: string | null
+    status: string | null
+    effort: string | null
+    priority: string | null
+    assignee: string | null
+    group: string | null
+    project: string
+    types: string[]
+}