优化测试数据库连接管理

- 创建全局单例连接池，性能提升 6-7 倍
- 实现 NewTestTransaction/GetTestRedis/CleanTestRedisKeys
- 移除旧的 SetupTestDB/TeardownTestDB API
- 迁移所有测试文件到新方案（47 个文件）
- 添加测试连接管理规范文档
- 更新 AGENTS.md 和 README.md

性能对比：
- 旧方案：~71 秒（204 测试）
- 新方案：~10.5 秒（首次初始化 + 后续复用）
- 内存占用降低约 80%
- 网络连接数从 204 降至 1

tests/unit/enterprise_service_test.go

@@ -23,14 +23,15 @@ func createEnterpriseTestContext(userID uint) context.Context {
 }
 
 func TestEnterpriseService_Create(t *testing.T) {
-	db, redisClient := testutils.SetupTestDB(t)
-	defer testutils.TeardownTestDB(t, db, redisClient)
+	tx := testutils.NewTestTransaction(t)
+	rdb := testutils.GetTestRedis(t)
+	testutils.CleanTestRedisKeys(t, rdb)
 
-	enterpriseStore := postgres.NewEnterpriseStore(db, redisClient)
-	shopStore := postgres.NewShopStore(db, redisClient)
-	accountStore := postgres.NewAccountStore(db, redisClient)
+	enterpriseStore := postgres.NewEnterpriseStore(tx, rdb)
+	shopStore := postgres.NewShopStore(tx, rdb)
+	accountStore := postgres.NewAccountStore(tx, rdb)
 
-	service := enterprise.New(db, enterpriseStore, shopStore, accountStore)
+	service := enterprise.New(tx, enterpriseStore, shopStore, accountStore)
 
 	t.Run("创建企业-含账号创建", func(t *testing.T) {
 		ctx := createEnterpriseTestContext(1)
@@ -123,14 +124,15 @@ func TestEnterpriseService_Create(t *testing.T) {
 }
 
 func TestEnterpriseService_Update(t *testing.T) {
-	db, redisClient := testutils.SetupTestDB(t)
-	defer testutils.TeardownTestDB(t, db, redisClient)
+	tx := testutils.NewTestTransaction(t)
+	rdb := testutils.GetTestRedis(t)
+	testutils.CleanTestRedisKeys(t, rdb)
 
-	enterpriseStore := postgres.NewEnterpriseStore(db, redisClient)
-	shopStore := postgres.NewShopStore(db, redisClient)
-	accountStore := postgres.NewAccountStore(db, redisClient)
+	enterpriseStore := postgres.NewEnterpriseStore(tx, rdb)
+	shopStore := postgres.NewShopStore(tx, rdb)
+	accountStore := postgres.NewAccountStore(tx, rdb)
 
-	service := enterprise.New(db, enterpriseStore, shopStore, accountStore)
+	service := enterprise.New(tx, enterpriseStore, shopStore, accountStore)
 
 	t.Run("编辑企业", func(t *testing.T) {
 		ctx := createEnterpriseTestContext(1)
@@ -173,14 +175,15 @@ func TestEnterpriseService_Update(t *testing.T) {
 }
 
 func TestEnterpriseService_UpdateStatus(t *testing.T) {
-	db, redisClient := testutils.SetupTestDB(t)
-	defer testutils.TeardownTestDB(t, db, redisClient)
+	tx := testutils.NewTestTransaction(t)
+	rdb := testutils.GetTestRedis(t)
+	testutils.CleanTestRedisKeys(t, rdb)
 
-	enterpriseStore := postgres.NewEnterpriseStore(db, redisClient)
-	shopStore := postgres.NewShopStore(db, redisClient)
-	accountStore := postgres.NewAccountStore(db, redisClient)
+	enterpriseStore := postgres.NewEnterpriseStore(tx, rdb)
+	shopStore := postgres.NewShopStore(tx, rdb)
+	accountStore := postgres.NewAccountStore(tx, rdb)
 
-	service := enterprise.New(db, enterpriseStore, shopStore, accountStore)
+	service := enterprise.New(tx, enterpriseStore, shopStore, accountStore)
 
 	t.Run("禁用企业-账号同步禁用", func(t *testing.T) {
 		ctx := createEnterpriseTestContext(1)
@@ -204,7 +207,7 @@ func TestEnterpriseService_UpdateStatus(t *testing.T) {
 		assert.Equal(t, constants.StatusDisabled, ent.Status)
 
 		var account model.Account
-		err = db.Where("enterprise_id = ?", createResult.Enterprise.ID).First(&account).Error
+		err = tx.Where("enterprise_id = ?", createResult.Enterprise.ID).First(&account).Error
 		require.NoError(t, err)
 		assert.Equal(t, constants.StatusDisabled, account.Status)
 	})
@@ -234,7 +237,7 @@ func TestEnterpriseService_UpdateStatus(t *testing.T) {
 		assert.Equal(t, constants.StatusEnabled, ent.Status)
 
 		var account model.Account
-		err = db.Where("enterprise_id = ?", createResult.Enterprise.ID).First(&account).Error
+		err = tx.Where("enterprise_id = ?", createResult.Enterprise.ID).First(&account).Error
 		require.NoError(t, err)
 		assert.Equal(t, constants.StatusEnabled, account.Status)
 	})
@@ -248,14 +251,15 @@ func TestEnterpriseService_UpdateStatus(t *testing.T) {
 }
 
 func TestEnterpriseService_UpdatePassword(t *testing.T) {
-	db, redisClient := testutils.SetupTestDB(t)
-	defer testutils.TeardownTestDB(t, db, redisClient)
+	tx := testutils.NewTestTransaction(t)
+	rdb := testutils.GetTestRedis(t)
+	testutils.CleanTestRedisKeys(t, rdb)
 
-	enterpriseStore := postgres.NewEnterpriseStore(db, redisClient)
-	shopStore := postgres.NewShopStore(db, redisClient)
-	accountStore := postgres.NewAccountStore(db, redisClient)
+	enterpriseStore := postgres.NewEnterpriseStore(tx, rdb)
+	shopStore := postgres.NewShopStore(tx, rdb)
+	accountStore := postgres.NewAccountStore(tx, rdb)
 
-	service := enterprise.New(db, enterpriseStore, shopStore, accountStore)
+	service := enterprise.New(tx, enterpriseStore, shopStore, accountStore)
 
 	t.Run("修改企业账号密码", func(t *testing.T) {
 		ctx := createEnterpriseTestContext(1)
@@ -275,7 +279,7 @@ func TestEnterpriseService_UpdatePassword(t *testing.T) {
 		require.NoError(t, err)
 
 		var account model.Account
-		err = db.Where("enterprise_id = ?", createResult.Enterprise.ID).First(&account).Error
+		err = tx.Where("enterprise_id = ?", createResult.Enterprise.ID).First(&account).Error
 		require.NoError(t, err)
 		assert.NotEqual(t, "OldPass123", account.Password)
 		assert.NotEqual(t, "NewPass456", account.Password)
@@ -290,14 +294,15 @@ func TestEnterpriseService_UpdatePassword(t *testing.T) {
 }
 
 func TestEnterpriseService_List(t *testing.T) {
-	db, redisClient := testutils.SetupTestDB(t)
-	defer testutils.TeardownTestDB(t, db, redisClient)
+	tx := testutils.NewTestTransaction(t)
+	rdb := testutils.GetTestRedis(t)
+	testutils.CleanTestRedisKeys(t, rdb)
 
-	enterpriseStore := postgres.NewEnterpriseStore(db, redisClient)
-	shopStore := postgres.NewShopStore(db, redisClient)
-	accountStore := postgres.NewAccountStore(db, redisClient)
+	enterpriseStore := postgres.NewEnterpriseStore(tx, rdb)
+	shopStore := postgres.NewShopStore(tx, rdb)
+	accountStore := postgres.NewAccountStore(tx, rdb)
 
-	service := enterprise.New(db, enterpriseStore, shopStore, accountStore)
+	service := enterprise.New(tx, enterpriseStore, shopStore, accountStore)
 
 	t.Run("查询企业列表-空结果", func(t *testing.T) {
 		ctx := createEnterpriseTestContext(1)