feat(leave) : show presence days in header for non-forfait, bound to contract start

Non-forfait header now shows '{weeklyHours} heures ({presence} présence)'.
Presence (presenceDaysByMonth/presenceDaysToToday) is bounded to the employee's
contract start so business days before hire are not counted (Dylan CDD: 43.5,
was 246). No change for employees present before the exercise or for forfait
(already capped at phase start). Leave summary now eager-loaded for any employee
with a leave tab to feed the header.

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

frontend/pages/employees/[id].vue

@@ -26,7 +26,7 @@
                     <p>Date d'entrée : {{ employee.entryDate ? employee.entryDate.split('-').reverse().join('/') : '-' }}</p>
                 </div>
                 <div class="text-right">
-                    <p class="font-bold text-[22px]">{{ contractNatureLabel(employee.currentContractNature) }} {{ employeeContractWorkLabel }}{{ forfaitRemainingDaysLabel }}</p>
+                    <p class="font-bold text-[22px]">{{ contractNatureLabel(employee.currentContractNature) }} {{ employeeContractWorkLabel }}{{ forfaitRemainingDaysLabel }}{{ nonForfaitPresenceLabel }}</p>
                     <p class="text-[18px]">{{ employee.site?.name ?? '-' }}</p>
                 </div>
             </div>
@@ -299,6 +299,7 @@ const {
     contractHistory,
     employeeContractWorkLabel,
     forfaitRemainingDaysLabel,
+    nonForfaitPresenceLabel,
     contractForm,
     createContractForm,
     isContractDrawerOpen,