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/composables/useCsvExport.ts

@@ -0,0 +1,44 @@
+export type CsvColumn<T> = {
+    header: string
+    value: (row: T) => string | number
+}
+
+/** Escapes a single CSV cell (quotes wrapping + doubled inner quotes). */
+function escapeCell(value: string | number): string {
+    const str = String(value ?? '')
+    if (/[",\n;]/.test(str)) {
+        return `"${str.replace(/"/g, '""')}"`
+    }
+    return str
+}
+
+export function useCsvExport() {
+    /** Builds a CSV string from rows + column definitions (semicolon separator, FR-friendly). */
+    function toCsv<T>(rows: T[], columns: CsvColumn<T>[]): string {
+        const header = columns.map(c => escapeCell(c.header)).join(';')
+        const lines = rows.map(row =>
+            columns.map(c => escapeCell(c.value(row))).join(';'),
+        )
+        return [header, ...lines].join('\n')
+    }
+
+    /** Triggers a browser download of the given CSV content. */
+    function downloadCsv<T>(filename: string, rows: T[], columns: CsvColumn<T>[]): void {
+        if (typeof window === 'undefined') {
+            return
+        }
+        const csv = toCsv(rows, columns)
+        // Prepend BOM so Excel detects UTF-8.
+        const blob = new Blob([`${csv}`], { type: 'text/csv;charset=utf-8;' })
+        const url = URL.createObjectURL(blob)
+        const link = document.createElement('a')
+        link.href = url
+        link.download = filename.endsWith('.csv') ? filename : `${filename}.csv`
+        document.body.appendChild(link)
+        link.click()
+        document.body.removeChild(link)
+        URL.revokeObjectURL(url)
+    }
+
+    return { toCsv, downloadCsv }
+}

frontend/modules/reporting/composables/useReportingFilters.ts

@@ -0,0 +1,41 @@
+export type ReportPeriodKey = 'thisMonth' | 'lastMonth' | 'custom'
+
+export type ReportPeriodRange = {
+    from: string
+    to: string
+}
+
+/** Formats a Date as an ISO "YYYY-MM-DD" string (local time, no timezone shift). */
+function toIsoDate(date: Date): string {
+    const year = date.getFullYear()
+    const month = String(date.getMonth() + 1).padStart(2, '0')
+    const day = String(date.getDate()).padStart(2, '0')
+    return `${year}-${month}-${day}`
+}
+
+/** Returns the {from, to} range (inclusive) for a given month offset relative to now. */
+function getMonthRange(offset: number): ReportPeriodRange {
+    const now = new Date()
+    const start = new Date(now.getFullYear(), now.getMonth() + offset, 1)
+    const end = new Date(now.getFullYear(), now.getMonth() + offset + 1, 0)
+    return { from: toIsoDate(start), to: toIsoDate(end) }
+}
+
+export function useReportingFilters() {
+    const thisMonth = (): ReportPeriodRange => getMonthRange(0)
+    const lastMonth = (): ReportPeriodRange => getMonthRange(-1)
+
+    /** Resolves a preset key to a concrete range. `custom` keeps the provided range. */
+    function rangeForPreset(key: ReportPeriodKey, current: ReportPeriodRange): ReportPeriodRange {
+        switch (key) {
+            case 'thisMonth':
+                return thisMonth()
+            case 'lastMonth':
+                return lastMonth()
+            case 'custom':
+                return current
+        }
+    }
+
+    return { thisMonth, lastMonth, rangeForPreset, toIsoDate }
+}