feat(project-management) : extract Projects/Tasks front into Nuxt module layer

Tranche 4 of LST-65. Companion to the backend module migration.

- Move pages (my-tasks, projects, projects/[id]/{index,groups,archives}),
  18 components (project + task), 10 services and 10 DTOs into
  frontend/modules/project-management/ (auto-detected layer).
- Rewrite explicit ~/services/* and ~/services/dto/* imports across 38
  consumers (admin tabs, mail modals, dashboard, mail page, layout) including
  the time-tracking module whose DTOs referenced project/task/task-tag.
- clients.ts and shared DTOs (client, user-data) stay at the root.
- Routes /my-tasks, /projects, /projects/:id(/groups|/archives) preserved;
  i18n stays global.

nuxt build passes; routes confirmed.

frontend/modules/project-management/services/task-groups.ts

@@ -0,0 +1,39 @@
+import type { TaskGroup, TaskGroupWrite } from './dto/task-group'
+import type { HydraCollection } from '~/utils/api'
+import { extractHydraMembers } from '~/utils/api'
+
+export function useTaskGroupService() {
+    const api = useApi()
+
+    async function getAll(): Promise<TaskGroup[]> {
+        const data = await api.get<HydraCollection<TaskGroup>>('/task_groups')
+        return extractHydraMembers(data)
+    }
+
+    async function getByProject(projectId: number): Promise<TaskGroup[]> {
+        const data = await api.get<HydraCollection<TaskGroup>>('/task_groups', {
+            project: `/api/projects/${projectId}`,
+        })
+        return extractHydraMembers(data)
+    }
+
+    async function create(payload: TaskGroupWrite): Promise<TaskGroup> {
+        return api.post<TaskGroup>('/task_groups', payload as Record<string, unknown>, {
+            toastSuccessKey: 'taskGroups.created',
+        })
+    }
+
+    async function update(id: number, payload: Partial<TaskGroupWrite>): Promise<TaskGroup> {
+        return api.patch<TaskGroup>(`/task_groups/${id}`, payload as Record<string, unknown>, {
+            toastSuccessKey: 'taskGroups.updated',
+        })
+    }
+
+    async function remove(id: number): Promise<void> {
+        await api.delete(`/task_groups/${id}`, {}, {
+            toastSuccessKey: 'taskGroups.deleted',
+        })
+    }
+
+    return { getAll, getByProject, create, update, remove }
+}