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/workflow.ts

@@ -0,0 +1,46 @@
+import type { TaskStatus, TaskStatusWrite } from './task-status'
+
+export type StatusCategory = 'todo' | 'in_progress' | 'blocked' | 'review' | 'done'
+
+export const STATUS_CATEGORY_LABEL: Record<StatusCategory, string> = {
+    todo: 'À faire',
+    in_progress: 'En cours',
+    blocked: 'Bloqué',
+    review: 'En validation',
+    done: 'Terminé',
+}
+
+/** Palette canonique des catégories (couleurs « classiques »), indépendante des workflows. */
+export const STATUS_CATEGORY_COLOR: Record<StatusCategory, string> = {
+    todo: '#222783',
+    in_progress: '#4A90D9',
+    blocked: '#C62828',
+    review: '#FF8F00',
+    done: '#26A69A',
+}
+
+/** Renvoie '#1f2937' (foncé) ou '#ffffff' (blanc) selon la luminance du fond, pour rester lisible. */
+export function contrastText(hex: string): string {
+    const c = hex.replace('#', '')
+    const r = parseInt(c.slice(0, 2), 16)
+    const g = parseInt(c.slice(2, 4), 16)
+    const b = parseInt(c.slice(4, 6), 16)
+    const lum = (0.299 * r + 0.587 * g + 0.114 * b) / 255
+    return lum > 0.6 ? '#1f2937' : '#ffffff'
+}
+
+export type Workflow = {
+    id: number
+    '@id'?: string
+    name: string
+    isDefault: boolean
+    position: number
+    statuses: TaskStatus[]
+}
+
+export type WorkflowWrite = {
+    name: string
+    isDefault: boolean
+    position: number
+    statuses?: TaskStatusWrite[]
+}