完善论坛配置与发帖体验：TipTap 富文本、图片上传、修订历史、Feed 排序与后台参数管理。

同步更新 README 与 ROADMAP，反映最新功能与开发状态。

Co-authored-by: Cursor <cursoragent@cursor.com>

service/upload.go

@@ -0,0 +1,53 @@
+package service
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"mime/multipart"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+)
+
+var allowedImageExt = map[string]bool{
+	".jpg":  true,
+	".jpeg": true,
+	".png":  true,
+	".gif":  true,
+	".webp": true,
+}
+
+// SaveUploadedImage 保存图片到本地目录，返回公开 URL 路径
+func SaveUploadedImage(file *multipart.FileHeader, dir, urlPrefix, namePrefix string) (string, error) {
+	ext := strings.ToLower(filepath.Ext(file.Filename))
+	if !allowedImageExt[ext] {
+		return "", errors.New("仅支持 jpg/png/gif/webp 格式")
+	}
+	if err := os.MkdirAll(dir, 0755); err != nil {
+		return "", err
+	}
+
+	filename := fmt.Sprintf("%s_%d%s", namePrefix, time.Now().UnixNano(), ext)
+	destPath := filepath.Join(dir, filename)
+
+	src, err := file.Open()
+	if err != nil {
+		return "", err
+	}
+	defer src.Close()
+
+	dst, err := os.Create(destPath)
+	if err != nil {
+		return "", err
+	}
+	defer dst.Close()
+
+	if _, err := io.Copy(dst, src); err != nil {
+		return "", err
+	}
+
+	prefix := strings.TrimSuffix(urlPrefix, "/")
+	return prefix + "/" + filename, nil
+}