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/mail/MailCreateTaskModal.vue

@@ -1,12 +1,12 @@
 <script setup lang="ts">
 import type { MailMessageDetailDto } from '~/services/dto/mail'
-import type { Task } from '~/services/dto/task'
-import type { Project } from '~/services/dto/project'
-import type { TaskGroup } from '~/services/dto/task-group'
+import type { Task } from '~/modules/project-management/services/dto/task'
+import type { Project } from '~/modules/project-management/services/dto/project'
+import type { TaskGroup } from '~/modules/project-management/services/dto/task-group'
 import type { UserData } from '~/services/dto/user-data'
 import { useMailService } from '~/services/mail'
-import { useProjectService } from '~/services/projects'
-import { useTaskGroupService } from '~/services/task-groups'
+import { useProjectService } from '~/modules/project-management/services/projects'
+import { useTaskGroupService } from '~/modules/project-management/services/task-groups'
 import { useUserService } from '~/services/users'
 import { useAuthStore } from '~/shared/stores/auth'