feat(leave) : align forfait CP N + display remaining workdays + N-1 absences exempt from presence

- LeaveRecapRowBuilder: forfait CP N now reflects remainingDays (acquis − pris depuis N) instead of the constant acquiredDays. Affects both PDF export and screen recap.
- Employee detail header: forfait label becomes "Forfait - 218 jours (X restants)" where X = 218 − presence days from Jan 1 to today (today included).
- New EmployeeLeaveSummary.presenceDaysToToday field, computed via the same logic as presenceDaysByMonth but capped at today.
- Forfait business rule: leaves attributed to N-1 stock no longer decrement presence days. Implemented by chronologically consuming an N-1 budget (= previousYearTakenDays) inside computePresenceDaysByMonth before counting any absence. Non-forfait unaffected (budget is 0).
- Doc updates: CLAUDE.md (forfait/N-1 rule), functional-rules.md (CP N forfait semantics).

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 }}</p>
+                    <p class="font-bold text-[22px]">{{ contractNatureLabel(employee.currentContractNature) }} {{ employeeContractWorkLabel }}{{ forfaitRemainingDaysLabel }}</p>
                     <p class="text-[18px]">{{ employee.site?.name ?? '-' }}</p>
                 </div>
             </div>
@@ -257,6 +257,7 @@ const {
     showRttTab,
     contractHistory,
     employeeContractWorkLabel,
+    forfaitRemainingDaysLabel,
     contractForm,
     createContractForm,
     isContractDrawerOpen,