feat: 配置 golangci-lint 静态分析并修复存量违规

- 新增 backend/.golangci.yml 配置 12 个 linter（forbidigo、errorlint、errcheck、staticcheck、revive、gocritic、gosec、bodyclose、noctx、nilerr、goimports、gocyclo）
- 新增 lefthook.yml 配置 pre-commit hook 自动运行 lint
- 修复存量代码违规：errors.Is/As 替换、zap.Error 替换、import 排序、errcheck 修复
- 更新 README 补充编码规范说明
- 归档 backend-code-lint 变更

backend/internal/service/service_supplemental_test.go

@@ -3,12 +3,12 @@ package service
 import (
 	"testing"
 
+	"nex/backend/internal/domain"
+	"nex/backend/internal/repository"
+
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"go.uber.org/zap"
-
-	"nex/backend/internal/domain"
-	"nex/backend/internal/repository"
 )
 
 func TestProviderService_Update(t *testing.T) {
@@ -133,7 +133,9 @@ func TestStatsService_Aggregate_Default(t *testing.T) {
 
 	totalCount := 0
 	for _, r := range result {
-		totalCount += r["request_count"].(int)
+		count, ok := r["request_count"].(int)
+		require.True(t, ok)
+		totalCount += count
 	}
 	assert.Equal(t, 15, totalCount)
 }