feat(leave) : resolve phase immediately preceding a given phase

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

src/State/EmployeeLeaveSummaryProvider.php

@@ -545,6 +545,25 @@ final readonly class EmployeeLeaveSummaryProvider implements ProviderInterface
         return $phases[0];
     }
 
+    /**
+     * Phase dont la date de début est la plus proche en deçà de celle de $phase
+     * (la phase qui précède immédiatement). Null si $phase est la première.
+     */
+    private function resolvePhaseImmediatelyBefore(Employee $employee, ContractPhase $phase): ?ContractPhase
+    {
+        $prior = null;
+        foreach ($this->phaseResolver->resolvePhases($employee) as $candidate) {
+            if ($candidate->startDate >= $phase->startDate) {
+                continue;
+            }
+            if (null === $prior || $candidate->startDate > $prior->startDate) {
+                $prior = $candidate;
+            }
+        }
+
+        return $prior;
+    }
+
     /**
      * @param list<ContractSuspension>                                      $suspensions
      * @param list<array{start: DateTimeImmutable, end: DateTimeImmutable}> $longMaladiePeriods