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/auth/session.go

@@ -4,6 +4,8 @@
 package auth
 
 import (
+	"Wavelet/core/contracts"
+	"Wavelet/pkg/config"
 	"context"
 	"crypto/sha256"
 	"encoding/hex"
@@ -15,9 +17,6 @@ import (
 	"github.com/gin-gonic/gin"
 	"github.com/google/uuid"
 	gsessions "github.com/gorilla/sessions"
-
-	"Wavelet/core/contracts"
-	"Wavelet/pkg/config"
 )
 
 // GetSessionOptions 根据配置构建 Session 选项