chore(lint): unify formatting on golangci-lint fmt (gofumpt), uncap issue reporting, fix gofumpt drift

- make format 现在与 code-check 使用同一格式化器（golangci-lint fmt），消除 goimports -local 与 gofumpt 的格式拉锯
- .golangci.yml 关闭默认 50/3 截断，完整上报所有问题（只增强不弱化）
- 全库 gofumpt 规范化（203 files, 纯格式无行为变更）

backend/plugins/infra/cache_memory/cache.go

@@ -4,13 +4,12 @@
 package cache_memory
 
 import (
-	"context"
-	"encoding/json"
-	"time"
-
 	"Wavelet/core"
 	"Wavelet/core/contracts"
 	"Wavelet/pkg/cache/ram"
+	"context"
+	"encoding/json"
+	"time"
 )
 
 type ramEntry struct {

backend/plugins/infra/cache_memory/plugin_test.go

@@ -4,16 +4,15 @@
 package cache_memory_test
 
 import (
+	"Wavelet/core"
+	"Wavelet/core/contracts"
+	"Wavelet/plugins/infra/cache_memory"
 	"context"
 	"testing"
 	"time"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
-
-	"Wavelet/core"
-	"Wavelet/core/contracts"
-	"Wavelet/plugins/infra/cache_memory"
 )
 
 func TestCacheMemoryPlugin(t *testing.T) {