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/driver-hours.vue

@@ -64,6 +64,7 @@
                     :get-row-metrics="getRowMetrics"
                     :get-row-absence-label="getRowAbsenceLabel"
                     :get-row-absence-style="getRowAbsenceStyle"
+                    :get-row-contract-nature="getRowContractNature"
                     :get-row-updated-at="getRowUpdatedAt"
                     :on-absence-click="openAbsenceDrawer"
                     :format-minutes="formatMinutes"
@@ -169,6 +170,7 @@ const {
   getRowMetrics,
   getRowAbsenceLabel,
   getRowAbsenceStyle,
+  getRowContractNature,
   getRowUpdatedAt,
   openAbsenceDrawer,
   submitAbsence,