功能: 集成 rclone 高级传输特性 + 全 70+ 后端支持

1. 失败自动重试：rclone Pacer 指数退避，默认 10 次底层 HTTP 重试
2. 带宽限制：配置 bandwidth_limit + Settings 运行时可调
3. 上传实时进度：progressReader + LogHub SSE 推送字节级进度/速率
4. 存储空间查询：StorageAbout 可选接口，GetUsage 返回远端真实空间
5. 全 rclone 后端：backend/all 引入 70+ 后端，新增 rclone 存储类型，
   API 驱动的可搜索后端选择器 + 动态配置表单

server/internal/backup/log_hub.go

@@ -1,6 +1,7 @@
 package backup
 
 import (
+	"fmt"
 	"sync"
 	"time"
 )
@@ -99,6 +100,41 @@ func (h *LogHub) Complete(recordID uint, status string) {
 	}
 }
 
+// AppendProgress 推送上传进度事件（节流：每个 recordID 每 500ms 最多一次，最终值始终推送）。
+func (h *LogHub) AppendProgress(recordID uint, progress ProgressInfo) {
+	h.mu.Lock()
+	defer h.mu.Unlock()
+	state := h.ensureState(recordID)
+
+	// 节流：距上次 progress 事件不足 500ms 且未完成则跳过（100% 始终推送）
+	now := time.Now().UTC()
+	isFinal := progress.Percent >= 100
+	if !isFinal && len(state.events) > 0 {
+		last := state.events[len(state.events)-1]
+		if last.Progress != nil && now.Sub(last.Timestamp) < 500*time.Millisecond {
+			return
+		}
+	}
+
+	state.nextSequence++
+	event := LogEvent{
+		RecordID:  recordID,
+		Sequence:  state.nextSequence,
+		Level:     "progress",
+		Message:   fmt.Sprintf("上传进度: %.1f%%", progress.Percent),
+		Timestamp: now,
+		Status:    state.status,
+		Progress:  &progress,
+	}
+	state.events = append(state.events, event)
+	for _, subscriber := range state.subscribers {
+		select {
+		case subscriber <- event:
+		default:
+		}
+	}
+}
+
 func (h *LogHub) ensureState(recordID uint) *logStreamState {
 	state, ok := h.streams[recordID]
 	if ok {

server/internal/backup/types.go

@@ -41,13 +41,23 @@ type RunResult struct {
 }
 
 type LogEvent struct {
-	RecordID  uint      `json:"recordId"`
-	Sequence  int64     `json:"sequence"`
-	Level     string    `json:"level"`
-	Message   string    `json:"message"`
-	Timestamp time.Time `json:"timestamp"`
-	Completed bool      `json:"completed"`
-	Status    string    `json:"status"`
+	RecordID  uint          `json:"recordId"`
+	Sequence  int64         `json:"sequence"`
+	Level     string        `json:"level"`
+	Message   string        `json:"message"`
+	Timestamp time.Time     `json:"timestamp"`
+	Completed bool          `json:"completed"`
+	Status    string        `json:"status"`
+	Progress  *ProgressInfo `json:"progress,omitempty"`
+}
+
+// ProgressInfo 描述上传进度，通过 SSE 实时推送给前端。
+type ProgressInfo struct {
+	BytesSent  int64   `json:"bytesSent"`
+	TotalBytes int64   `json:"totalBytes"`
+	Percent    float64 `json:"percent"`
+	SpeedBps   float64 `json:"speedBps"`   // bytes/sec
+	TargetName string  `json:"targetName"`
 }
 
 type LogWriter interface {