feat : sélecteur d'exercice sur l'onglet RTT de la fiche employé

Permet de consulter les exercices passés (table hebdomadaire RTT) en
réutilisant le pattern de l'onglet Congés. Plage bornée par
max(début historique contrat, RTT_START_DATE). Bouton + Payer les RTT
verrouillé sur exercices clos. Onglet masqué pour FORFAIT (inchangé).

Backend : rttStartDate désormais toujours exposé sur EmployeeRttSummary
pour que le sélecteur conserve sa borne lors de la navigation vers un
exercice passé. Le masquage existant des lignes Report continue de
fonctionner (comparaison mois-à-mois).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/components/employees/RttTab.vue

@@ -11,7 +11,7 @@
           <Icon name="mdi:chevron-left" size="24"/>
         </button>
         <span class="text-lg font-bold tracking-wide min-w-[170px] text-center">
-          {{ currentMonthLabel }} {{ currentYear }}
+          {{ currentMonthLabel }} {{ displayedMonthYear }}
         </span>
         <button
           class="rounded px-2 py-1 font-bold hover:bg-primary-600 disabled:opacity-40 disabled:cursor-not-allowed flex items-center"
@@ -27,7 +27,8 @@
       </p>
         <div class="flex justify-center">
             <button
-                class="rounded-md bg-primary-500 px-8 py-2 font-bold text-white hover:bg-primary-600"
+                class="rounded-md bg-primary-500 px-8 py-2 font-bold text-white hover:bg-primary-600 disabled:opacity-40 disabled:cursor-not-allowed"
+                :disabled="isHistoricalYear"
                 @click="openPaymentDrawer"
             >
                 + Payer les RTT
@@ -183,6 +184,22 @@
           </tr>
         </tbody>
       </table>
+      <div class="mt-6 flex items-center gap-3">
+        <label for="rtt-year-select" class="text-md font-semibold text-primary-500 uppercase">
+          Exercice :
+        </label>
+        <select
+          id="rtt-year-select"
+          :value="selectedYear ?? ''"
+          :disabled="!availableYears.length"
+          class="border border-primary-500 rounded-md px-3 py-1 text-md font-semibold text-primary-500 bg-white focus:outline-none focus:ring-2 focus:ring-secondary-500/20 disabled:opacity-50"
+          @change="handleYearChange"
+        >
+          <option v-for="option in availableYears" :key="option.value" :value="option.value">
+            {{ option.label }}
+          </option>
+        </select>
+      </div>
     </div>
 
     <!-- Payment Drawer -->
@@ -261,14 +278,36 @@
 import type { EmployeeRttSummary, EmployeeRttWeekSummary } from '~/services/dto/employee-rtt-summary'
 import AppDrawer from '~/components/AppDrawer.vue'
 
+type RttYearOption = {
+  value: number
+  label: string
+}
+
 const props = defineProps<{
   summary: EmployeeRttSummary | null
+  selectedYear: number | null
+  availableYears: RttYearOption[]
+  currentYear: number | null
 }>()
 
 const emit = defineEmits<{
   (event: 'submit-rtt-payment', month: number, base25Minutes: number, bonus25Minutes: number, base50Minutes: number, bonus50Minutes: number): void
+  (event: 'update-selected-year', year: number): void
 }>()
 
+const isHistoricalYear = computed(() =>
+  props.selectedYear !== null
+  && props.currentYear !== null
+  && props.selectedYear !== props.currentYear
+)
+
+const handleYearChange = (event: Event) => {
+  const target = event.target as HTMLSelectElement
+  const value = Number(target.value)
+  if (Number.isNaN(value)) return
+  emit('update-selected-year', value)
+}
+
 // --- Last complete week number ---
 
 const lastCompleteWeek = computed(() => {
@@ -324,7 +363,7 @@ const currentMonth = computed(() => orderedMonths[currentMonthIndex.value])
 
 const currentMonthLabel = computed(() => monthLabels[currentMonth.value])
 
-const currentYear = computed(() => {
+const displayedMonthYear = computed(() => {
   if (!props.summary) return ''
   return currentMonth.value >= 6 ? props.summary.year - 1 : props.summary.year
 })