add refund logic and fix books inventory logic

app/Services/SchoolYearValidationService.php

@@ -42,6 +42,14 @@ final class SchoolYearValidationService
         }
 
         $this->dateOrNull($payload['fall_makeup_exam_on'] ?? null);
+
+        $weeks = $payload['total_instructional_weeks'] ?? null;
+        if ($weeks !== null && trim((string) $weeks) !== '') {
+            $parsed = filter_var($weeks, FILTER_VALIDATE_INT);
+            if ($parsed === false || $parsed <= 0) {
+                throw new InvalidArgumentException('Total instructional weeks must be a positive whole number.');
+            }
+        }
     }
 
     public function isValidYearName(string $value): bool