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/conversion/openai/adapter_test.go

@@ -48,10 +48,10 @@ func TestAdapter_BuildUrl(t *testing.T) {
 	a := NewAdapter()
 
 	tests := []struct {
-		name         string
-		nativePath   string
+		name          string
+		nativePath    string
 		interfaceType conversion.InterfaceType
-		expected     string
+		expected      string
 	}{
 		{"聊天", "/chat/completions", conversion.InterfaceTypeChat, "/chat/completions"},
 		{"模型", "/models", conversion.InterfaceTypeModels, "/models"},
@@ -92,9 +92,9 @@ func TestAdapter_SupportsInterface(t *testing.T) {
 	a := NewAdapter()
 
 	tests := []struct {
-		name         string
+		name          string
 		interfaceType conversion.InterfaceType
-		expected     bool
+		expected      bool
 	}{
 		{"聊天", conversion.InterfaceTypeChat, true},
 		{"模型", conversion.InterfaceTypeModels, true},