feat : sélecteur d'année sur l'onglet Congés de la fiche employé

Permet de consulter les exercices passés (calendrier + compteurs) sur
l'onglet Congés. La plage proposée est bornée par max(début historique
contrat, RTT_START_DATE) pour ne pas remonter avant la mise en service
du logiciel. Édition des stocks N-1 et fractionnés verrouillée sur
exercices clos.

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

frontend/components/employees/LeaveTab.vue

@@ -39,6 +39,8 @@
                 </div>
                 <button
                     class="flex items-center"
+                    :class="isHistoricalYear ? 'opacity-40 cursor-not-allowed' : ''"
+                    :disabled="isHistoricalYear"
                     @click="openPaidLeaveDrawer"
                 >
                     <Icon name="mdi:edit-box" size="24"/>
@@ -51,6 +53,8 @@
                 </div>
                 <button
                     class="flex items-center"
+                    :class="isHistoricalYear ? 'opacity-40 cursor-not-allowed' : ''"
+                    :disabled="isHistoricalYear"
                     @click="openFractionedDrawer"
                 >
                     <Icon name="mdi:edit-box" size="24"/>
@@ -90,6 +94,22 @@
                     </div>
                 </div>
             </div>
+            <div class="mt-6 flex items-center gap-3">
+                <label for="leave-year-select" class="text-md font-semibold text-primary-500 uppercase">
+                    {{ isForfaitRule ? 'Année :' : 'Exercice :' }}
+                </label>
+                <select
+                    id="leave-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>
         <AppDrawer v-model="isFractionedDrawerOpen" title="Jours fractionnés">
             <form class="space-y-4" @submit.prevent="handleSubmitFractioned">
@@ -173,17 +193,39 @@ type DayLeaveState = {
     colors: string[]
 }
 
+type LeaveYearOption = {
+    value: number
+    label: string
+}
+
 const props = defineProps<{
     absences: Absence[]
     summary: EmployeeLeaveSummary | null
     publicHolidays: Record<string, string>
+    selectedYear: number | null
+    availableYears: LeaveYearOption[]
+    currentYear: number | null
 }>()
 
 const emit = defineEmits<{
     (event: 'update-fractioned-days', days: number): void
     (event: 'update-paid-leave-days', days: 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)
+}
+
 const isFractionedDrawerOpen = ref(false)
 const fractionedForm = reactive({days: 0})
 
@@ -239,6 +281,7 @@ const currentYearTakenDays = computed(() => {
 })
 
 const displayedYear = computed(() => {
+    if (props.selectedYear) return props.selectedYear
     if (props.summary?.year) return props.summary.year
     const today = new Date()
     const year = today.getFullYear()