feat(absence) : extract Absence front into Nuxt module layer

LST-66 (2.3) front. Companion to the backend module migration.

- Move pages (absences, team-absences), 8 components, the absences service +
  DTO and the useAbsenceHelpers composable into frontend/modules/absence/
  (auto-detected layer; composable now auto-imported).
- Rewrite consumers: AdminAbsencePolicyTab and the time-tracking calendar
  (getPublicHolidays) point to ~/modules/absence/...
- Middlewares (employee/admin) and shared services (clients, users,
  user-data DTO) stay at the root. i18n stays global.
- Routes /absences and /team-absences preserved.

nuxt build passes; routes confirmed.

frontend/modules/absence/services/dto/absence.ts

@@ -0,0 +1,93 @@
+export type AbsenceType = 'cp' | 'mariage_pacs' | 'naissance' | 'conge_parental' | 'deces' | 'maladie'
+export type AbsenceStatus = 'pending' | 'approved' | 'rejected' | 'cancelled'
+export type HalfDay = 'matin' | 'apres_midi'
+
+export type AbsenceUserRef = {
+    '@id'?: string
+    id: number
+    username: string
+    avatarUrl: string | null
+}
+
+export type AbsenceRequest = {
+    '@id'?: string
+    id: number
+    user: AbsenceUserRef
+    type: AbsenceType
+    label: string
+    startDate: string
+    endDate: string
+    startHalfDay: HalfDay | null
+    endHalfDay: HalfDay | null
+    countedDays: number
+    reason: string | null
+    justificationFileName: string | null
+    justificationUrl: string | null
+    status: AbsenceStatus
+    rejectionReason: string | null
+    createdAt: string
+    reviewedAt: string | null
+    reviewedBy: AbsenceUserRef | null
+}
+
+export type AbsenceRequestWrite = {
+    type: AbsenceType
+    startDate: string
+    endDate: string
+    startHalfDay?: HalfDay | null
+    endHalfDay?: HalfDay | null
+    reason?: string | null
+}
+
+export type AbsenceBalance = {
+    '@id'?: string
+    id: number
+    user: AbsenceUserRef
+    type: AbsenceType
+    label: string
+    period: string
+    acquired: number
+    acquiring: number
+    acquiredTotal: number
+    taken: number
+    pending: number
+    available: number
+}
+
+export type AbsencePolicy = {
+    '@id'?: string
+    id: number
+    type: AbsenceType
+    label: string
+    daysPerYear: number | null
+    daysPerEvent: number | null
+    justificationRequired: boolean
+    noticeDays: number
+    countWorkingDaysOnly: boolean
+    active: boolean
+}
+
+export type AbsencePolicyWrite = {
+    daysPerYear?: number | null
+    daysPerEvent?: number | null
+    justificationRequired?: boolean
+    noticeDays?: number
+    countWorkingDaysOnly?: boolean
+    active?: boolean
+}
+
+export type AbsencePreviewPayload = {
+    type: AbsenceType
+    startDate: string
+    endDate: string
+    startHalfDay?: HalfDay | null
+    endHalfDay?: HalfDay | null
+}
+
+export type AbsencePreviewResult = {
+    countedDays: number
+    period: string | null
+    available: number | null
+    projectedAvailable: number | null
+    justificationRequired: boolean
+}