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/tasks.ts

@@ -0,0 +1,34 @@
+import type { Task, TaskWrite } from './dto/task'
+import type { HydraCollection } from '~/utils/api'
+import { extractHydraMembers } from '~/utils/api'
+
+export function useTaskService() {
+    const api = useApi()
+
+    async function getByProject(projectId: number): Promise<Task[]> {
+        const data = await api.get<HydraCollection<Task>>('/tasks', {
+            project: `/api/projects/${projectId}`,
+        })
+        return extractHydraMembers(data)
+    }
+
+    async function create(payload: TaskWrite): Promise<Task> {
+        return api.post<Task>('/tasks', payload as Record<string, unknown>, {
+            toastSuccessKey: 'tasks.created',
+        })
+    }
+
+    async function update(id: number, payload: Partial<TaskWrite>): Promise<Task> {
+        return api.patch<Task>(`/tasks/${id}`, payload as Record<string, unknown>, {
+            toastSuccessKey: 'tasks.updated',
+        })
+    }
+
+    async function remove(id: number): Promise<void> {
+        await api.delete(`/tasks/${id}`, {}, {
+            toastSuccessKey: 'tasks.deleted',
+        })
+    }
+
+    return { getByProject, create, update, remove }
+}