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/routing_cache.go

@@ -4,10 +4,11 @@ import (
 	"strings"
 	"sync"
 
-	"go.uber.org/zap"
-
 	"nex/backend/internal/domain"
 	"nex/backend/internal/repository"
+
+	"go.uber.org/zap"
+
 	pkglogger "nex/backend/pkg/logger"
 )
 
@@ -34,7 +35,9 @@ func NewRoutingCache(
 
 func (c *RoutingCache) GetProvider(id string) (*domain.Provider, error) {
 	if v, ok := c.providers.Load(id); ok {
-		return v.(*domain.Provider), nil
+		if provider, ok := v.(*domain.Provider); ok {
+			return provider, nil
+		}
 	}
 
 	provider, err := c.providerRepo.GetByID(id)
@@ -43,7 +46,9 @@ func (c *RoutingCache) GetProvider(id string) (*domain.Provider, error) {
 	}
 
 	if v, ok := c.providers.Load(id); ok {
-		return v.(*domain.Provider), nil
+		if provider, ok := v.(*domain.Provider); ok {
+			return provider, nil
+		}
 	}
 
 	c.providers.Store(id, provider)
@@ -54,7 +59,9 @@ func (c *RoutingCache) GetModel(providerID, modelName string) (*domain.Model, er
 	key := providerID + "/" + modelName
 
 	if v, ok := c.models.Load(key); ok {
-		return v.(*domain.Model), nil
+		if model, ok := v.(*domain.Model); ok {
+			return model, nil
+		}
 	}
 
 	model, err := c.modelRepo.FindByProviderAndModelName(providerID, modelName)
@@ -63,7 +70,9 @@ func (c *RoutingCache) GetModel(providerID, modelName string) (*domain.Model, er
 	}
 
 	if v, ok := c.models.Load(key); ok {
-		return v.(*domain.Model), nil
+		if model, ok := v.(*domain.Model); ok {
+			return model, nil
+		}
 	}
 
 	c.models.Store(key, model)
@@ -97,7 +106,12 @@ func (c *RoutingCache) invalidateModelsByProvider(providerID string) {
 	prefix := providerID + "/"
 	count := 0
 	c.models.Range(func(key, value interface{}) bool {
-		if strings.HasPrefix(key.(string), prefix) {
+		keyStr, ok := key.(string)
+		if !ok {
+			return true
+		}
+
+		if strings.HasPrefix(keyStr, prefix) {
 			c.models.Delete(key)
 			count++
 		}