feat(leave) : prorate forfait work-target days in employee header

The header hardcoded '218 jours' and '218 - presence restants', wrong for a
forfait entered mid-year. Expose forfaitWorkTargetDays = businessDays(period) -
acquiredDays (218 full year, prorated otherwise) and show
'Forfait - {target} jours ({presence} présence · {target-presence} restants)'.
Grégory: 155 jours (11 présence · 144 restants).

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

src/State/EmployeeLeaveSummaryProvider.php

@@ -133,6 +133,14 @@ final readonly class EmployeeLeaveSummaryProvider implements ProviderInterface
         $summary->previousYearPaidDays      = $paidLeaveDays;
 
         [$periodFrom, $periodTo] = $this->resolvePeriodBounds($employee, $year, $phase);
+
+        // Forfait : jours à travailler sur l'exercice = jours ouvrés de la période − congés acquis.
+        // Année pleine → 218 (252 − 34) ; entrée en cours d'année → prorata (ex. 168 − 13 ≈ 155).
+        if (LeaveRuleCode::FORFAIT_218->value === $summary->ruleCode) {
+            $businessDaysInPeriod           = $this->countBusinessDays($periodFrom, $periodTo, $this->buildRawPublicHolidayMap($periodFrom, $periodTo));
+            $summary->forfaitWorkTargetDays = $businessDaysInPeriod - $summary->acquiredDays;
+        }
+
         // Forfait-only: leaves taken from N-1 stock do NOT decrement presence days.
         // For non-forfait, previousYearTakenDays is always 0, so the budget has no effect.
         $n1AbsencesBudget             = $yearSummary['previousYearTakenDays'];