feat : migrate filter/form UI to @malio/layer-ui + fix hours/calendar contract scoping

- Add @malio/layer-ui as Nuxt layer (extends in nuxt.config.ts)
- Migrate site/employee/contract filters to MalioSelectCheckbox / MalioInputText / MalioSelect on employees, calendar and hours screens
- Migrate absence drawer selects + submit button to Malio (MalioSelect + MalioButton)
- Migrate calendar "Ajouter une absence" / "Imprimer" actions to MalioButton
- Drop now-unused EmployeeNameFilterInput and SiteFilterSelector components
- Hours day view: resolve contract nature at selected date (WorkHourDayContext.contractNature) instead of employee.currentContractNature (today-based); fixes interim contracts showing as CDI when mission ended
- Calendar: hide employees whose contract periods do not intersect the displayed month
- Layout: scrollbar-gutter:stable on <main> to avoid horizontal shift when dropdowns open
- Update functional-rules.md, in-app documentation, CLAUDE.md to match

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

frontend/pages/employees/index.vue

@@ -34,19 +34,29 @@
                     </button>
                 </div>
             </div>
-            <div class="flex gap-3 py-7">
+            <div class="flex items-center gap-3 py-7">
                 <div class="w-80">
-                    <EmployeeNameFilterInput v-model="employeeFilter"/>
+                    <MalioInputText
+                        v-model="employeeFilter"
+                        label="Recherche d'un employé"
+                        icon-name="mdi:magnify"
+                    />
                 </div>
-                <SiteFilterSelector v-if="sites.length > 0" v-model="selectedSiteIds" :sites="sites"/>
-                <select
+                <div v-if="sites.length > 0" class="relative z-50 w-80">
+                    <MalioSelectCheckbox
+                        v-model="selectedSiteIds"
+                        :options="siteOptions"
+                        label="Sites"
+                        display-select-all
+                    />
+                </div>
+
+                <MalioSelect
                     v-model="contractStatusFilter"
-                    class="rounded-md border border-primary-500 bg-white px-3 py-2 text-md font-semibold text-primary-500 cursor-pointer"
-                >
-                    <option value="active">Avec contrat</option>
-                    <option value="inactive">Sans contrat</option>
-                    <option value="all">Tous</option>
-                </select>
+                    label="Statut contrat"
+                    :options="contractStatusOptions"
+                    group-class="w-40"
+                />
             </div>
         </div>
 
@@ -275,7 +285,6 @@ import {listContracts} from '~/services/contracts'
 import {createEmployee, deleteEmployee, listEmployees, updateEmployee} from '~/services/employees'
 import {listSites} from '~/services/sites'
 import {listInterimAgencies, type InterimAgency} from '~/services/interim-agencies'
-import SiteFilterSelector from '~/components/SiteFilterSelector.vue'
 import SalaryRecapDrawer from '~/components/SalaryRecapDrawer.vue'
 import BulkYearlyHoursDrawer from '~/components/BulkYearlyHoursDrawer.vue'
 import {contractNatureLabel, isContractNature, requiresContractEndDate, showsContractEndDate} from '~/utils/contract'
@@ -304,7 +313,13 @@ const contracts = ref<Contract[]>([])
 const interimAgencies = ref<InterimAgency[]>([])
 const employeeFilter = ref('')
 const contractStatusFilter = ref<'active' | 'inactive' | 'all'>('active')
+const contractStatusOptions = [
+    { label: 'Avec contrat', value: 'active' },
+    { label: 'Sans contrat', value: 'inactive' },
+    { label: 'Tous', value: 'all' }
+]
 const selectedSiteIds = ref<number[]>([])
+const siteOptions = computed(() => sites.value.map((site) => ({ label: site.name, value: site.id })))
 
 const filteredEmployees = computed<Employee[]>(() => {
     if (selectedSiteIds.value.length === 0) return []