feat(reporting) : add Reporting dashboard front layer

LST-59 (3.1) front. Completes the Reporting module.

- New frontend/modules/reporting/ layer (auto-detected): /reporting page
  (admin middleware) consuming the 4 read-only report endpoints.
- Filters (period presets + custom dates, project, user). 4 sections (time per
  project, time per user, tasks by status, absences by type) each with a
  DataTable + a Chart.js chart (reused global registration).
- Front-side CSV export per section (useCsvExport: BOM UTF-8, ; separator).
- i18n keys (reporting.*, sidebar.admin.reporting).

nuxt build passes; /reporting routed; no route regression.

frontend/modules/reporting/services/reporting.ts

@@ -0,0 +1,51 @@
+import type {
+    AbsencesByType,
+    ReportFilters,
+    TasksByStatus,
+    TimePerProject,
+    TimePerUser,
+} from './dto/reporting'
+import type { AnyObject } from '~/shared/composables/useApi'
+import type { HydraCollection } from '~/utils/api'
+import { extractHydraMembers } from '~/utils/api'
+
+function buildQuery(filters: Partial<ReportFilters>, keys: (keyof ReportFilters)[]): AnyObject {
+    const query: AnyObject = {}
+    for (const key of keys) {
+        const value = filters[key]
+        if (value !== undefined && value !== null && value !== '') {
+            query[key] = value
+        }
+    }
+    return query
+}
+
+export function useReportingService() {
+    const api = useApi()
+
+    async function timePerProject(filters: ReportFilters): Promise<TimePerProject[]> {
+        const query = buildQuery(filters, ['from', 'to', 'userId', 'projectId'])
+        const data = await api.get<HydraCollection<TimePerProject>>('/reports/time-per-project', query, { toast: false })
+        return extractHydraMembers(data)
+    }
+
+    async function timePerUser(filters: ReportFilters): Promise<TimePerUser[]> {
+        const query = buildQuery(filters, ['from', 'to', 'projectId'])
+        const data = await api.get<HydraCollection<TimePerUser>>('/reports/time-per-user', query, { toast: false })
+        return extractHydraMembers(data)
+    }
+
+    async function tasksByStatus(filters: ReportFilters): Promise<TasksByStatus[]> {
+        const query = buildQuery(filters, ['projectId'])
+        const data = await api.get<HydraCollection<TasksByStatus>>('/reports/tasks-by-status', query, { toast: false })
+        return extractHydraMembers(data)
+    }
+
+    async function absencesByType(filters: ReportFilters): Promise<AbsencesByType[]> {
+        const query = buildQuery(filters, ['from', 'to', 'userId'])
+        const data = await api.get<HydraCollection<AbsencesByType>>('/reports/absences-by-type', query, { toast: false })
+        return extractHydraMembers(data)
+    }
+
+    return { timePerProject, timePerUser, tasksByStatus, absencesByType }
+}