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/domain/system/plugin.go

@@ -5,15 +5,14 @@
 package system
 
 import (
-	"net/http"
-	"reflect"
-
-	"github.com/gin-gonic/gin"
-
 	"Wavelet/core"
 	"Wavelet/core/contracts"
 	"Wavelet/pkg/config"
 	"Wavelet/pkg/response"
+	"net/http"
+	"reflect"
+
+	"github.com/gin-gonic/gin"
 )
 
 // Plugin implements core.Plugin to provide system-level basic routes.