test: 프론트엔드/백엔드 테스트 커버리지 및 시나리오 보강 (Issue #291)

- FE: Vitest 환경 구축 및 공통 UI 컴포넌트(Badge, Button) 테스트 추가
- FE: Playwright E2E 테스트(Auth, Tenant CRUD 및 Validation) 시나리오 보강
- BE: Testcontainers 기반 Repository 통합 테스트(PostgreSQL) 추가
- BE: TenantRepository 계층 구조(Hierarchy), DB 제약조건(Unique) 테스트
- BE: UserRepository 통합 테스트(CRUD, Delete) 추가
- BE: PasswordPolicy 유틸리티 테스트 보강
- BE: TenantService 엣지 케이스(중복 슬러그, 권한 등) 검증 로직 추가
- Fix: 하위 테넌트 생성 시 ParentID 누락 문제 해결

backend/internal/repository/main_test.go

@@ -0,0 +1,69 @@
+package repository
+
+import (
+	"context"
+	"log"
+	"os"
+	"testing"
+	"time"
+
+	"baron-sso-backend/internal/domain"
+
+	"github.com/testcontainers/testcontainers-go"
+	postgres_module "github.com/testcontainers/testcontainers-go/modules/postgres"
+	"github.com/testcontainers/testcontainers-go/wait"
+	gorm_postgres "gorm.io/driver/postgres"
+	"gorm.io/gorm"
+)
+
+var testDB *gorm.DB
+
+func TestMain(m *testing.M) {
+	ctx := context.Background()
+
+	// Start PostgreSQL container
+	dbName := "testdb"
+	dbUser := "user"
+	dbPassword := "password"
+
+	postgresContainer, err := postgres_module.Run(ctx,
+		"postgres:16-alpine",
+		postgres_module.WithDatabase(dbName),
+		postgres_module.WithUsername(dbUser),
+		postgres_module.WithPassword(dbPassword),
+		testcontainers.WithWaitStrategy(
+			wait.ForLog("database system is ready to accept connections").
+				WithOccurrence(2).
+				WithStartupTimeout(30*time.Second)),
+	)
+	if err != nil {
+		log.Fatalf("failed to start container: %s", err)
+	}
+
+	defer func() {
+		if err := postgresContainer.Terminate(ctx); err != nil {
+			log.Fatalf("failed to terminate container: %s", err)
+		}
+	}()
+
+	connStr, err := postgresContainer.ConnectionString(ctx, "sslmode=disable")
+	if err != nil {
+		log.Fatalf("failed to get connection string: %s", err)
+	}
+
+	// Connect to test database
+	db, err := gorm.Open(gorm_postgres.Open(connStr), &gorm.Config{})
+	if err != nil {
+		log.Fatalf("failed to connect to database: %s", err)
+	}
+
+	// Auto-migrate
+	err = db.AutoMigrate(&domain.Tenant{}, &domain.TenantDomain{}, &domain.User{})
+	if err != nil {
+		log.Fatalf("failed to migrate database: %s", err)
+	}
+
+	testDB = db
+
+	os.Exit(m.Run())
+}