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/dto/task-group.ts

@@ -0,0 +1,19 @@
+import type { Project } from './project'
+
+export type TaskGroup = {
+    id: number
+    '@id'?: string
+    title: string
+    description: string | null
+    color: string
+    project: Project | null
+    archived: boolean
+}
+
+export type TaskGroupWrite = {
+    title: string
+    description: string | null
+    color: string
+    project: string
+    archived?: boolean
+}