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/components/admin/AdminWorkflowTab.vue

@@ -42,8 +42,8 @@
 </template>
 
 <script setup lang="ts">
-import type { Workflow } from '~/services/dto/workflow'
-import { useWorkflowService } from '~/services/workflows'
+import type { Workflow } from '~/modules/project-management/services/dto/workflow'
+import { useWorkflowService } from '~/modules/project-management/services/workflows'
 import type { DataTableColumn } from '~/components/ui/DataTable.vue'
 
 const { t } = useI18n()