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/upload/util/media.go

@@ -4,9 +4,8 @@
 package util
 
 import (
-	"strings"
-
 	"Wavelet/plugins/domain/upload/shared"
+	"strings"
 )
 
 // IsImageExtension reports whether ext is a common image format.

backend/plugins/domain/upload/util/utils.go

@@ -5,20 +5,19 @@
 package util
 
 import (
+	"Wavelet/plugins/domain/upload/shared"
 	"bytes"
 	"errors"
 	"fmt"
-	"image"
-	_ "image/gif"  // Register GIF decoder for image.Decode
-	_ "image/jpeg" // Register JPEG decoder for image.Decode
-	_ "image/png"  // Register PNG decoder for image.Decode
+	"image"        // Register GIF decoder for image.Decode
+	_ "image/gif"  // Register JPEG decoder for image.Decode
+	_ "image/jpeg" // Register PNG decoder for image.Decode
+	_ "image/png"
 	"io"
 	"strings"
 
 	"github.com/deepteams/webp"
 	_ "golang.org/x/image/webp" // Register WebP decoder for image.Decode
-
-	"Wavelet/plugins/domain/upload/shared"
 )
 
 // ValidateS3Key validates an S3 object key for safety.