Add aftersales stats to dashboard and service-layer tests

- CompanyStatsOverviewDTO and GetStats() now include aftersales counts
  (total, pending confirmation, closed, rejected) and a recentAftersales list
- aftersales_service_test.go covers YYMMNN sequence, owner-only submit,
  state machine, phone last-4 check, reject increment, force-close
- users_service_test.go covers duplicate username, self-demotion guard,
  last-admin guard, password reset, assignable filter

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

services/services_test.go

@@ -32,6 +32,7 @@ func TestMain(m *testing.M) {
 	database.DB.Unscoped().Where("1 = 1").Delete(&models.Company{})
 	database.DB.Unscoped().Where("1 = 1").Delete(&models.Serial{})
 	database.DB.Unscoped().Where("1 = 1").Delete(&models.EmployeeSerial{})
+	database.DB.Unscoped().Where("1 = 1").Delete(&models.AftersalesOrder{})
 
 	exitCode := m.Run()
 
@@ -39,6 +40,7 @@ func TestMain(m *testing.M) {
 	database.DB.Unscoped().Where("1 = 1").Delete(&models.Company{})
 	database.DB.Unscoped().Where("1 = 1").Delete(&models.Serial{})
 	database.DB.Unscoped().Where("1 = 1").Delete(&models.EmployeeSerial{})
+	database.DB.Unscoped().Where("1 = 1").Delete(&models.AftersalesOrder{})
 
 	os.Exit(exitCode)
 }