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/components/driver-hours/DriverHoursDayView.vue

@@ -43,7 +43,7 @@
                         </p>
                         <p class="text-neutral-500 truncate inline-flex items-center gap-2">
                             <span>
-                                {{ employee.site?.name ?? 'Sans site' }}<span v-if="employee.currentContractNature"> — {{ contractNatureLabel(employee.currentContractNature) }}</span>
+                                {{ employee.site?.name ?? 'Sans site' }}<span v-if="getRowContractNature(employee.id)"> — {{ contractNatureLabel(getRowContractNature(employee.id) ?? undefined) }}</span>
                             </span>
                             <span
                                 v-if="isAdmin && (rows[employee.id]?.isSiteValid ?? false)"
@@ -205,6 +205,7 @@ const props = defineProps<{
     getRowMetrics: (employeeId: number) => { dayMinutes: number; nightMinutes: number; workshopMinutes: number; totalMinutes: number; virtualHolidayMinutes: number }
     getRowAbsenceLabel: (employeeId: number) => string
     getRowAbsenceStyle: (employeeId: number) => { backgroundColor: string } | undefined
+    getRowContractNature: (employeeId: number) => 'CDI' | 'CDD' | 'INTERIM' | null
     getRowUpdatedAt: (employeeId: number) => string
     onAbsenceClick: (employeeId: number) => void
     formatMinutes: (minutes: number) => string