重构: 存储传输层集成 rclone 替代自研实现

将 8 种存储后端（本地磁盘、S3、WebDAV、Google Drive、FTP、阿里云 OSS、
腾讯云 COS、七牛 Kodo）的底层传输从 4 个独立 SDK 自研实现替换为 rclone
fs 接口统一驱动。

- 新建 storage/rclone/ 包（~410 行胶水代码），包含通用 Provider 和 8 种
  配置映射 Factory
- 删除 10 个旧 provider 包（~1000 行），净减少约 1000 行代码
- StorageProvider 接口、前端 UI、数据库模型、备份执行引擎全部零改动
- 获得 rclone 工业级传输能力（分片上传、断点续传、自动重试）

server/internal/storage/rclone/provider_test.go

@@ -0,0 +1,129 @@
+package rclone
+
+import (
+	"context"
+	"io"
+	"strings"
+	"testing"
+)
+
+func TestProviderLocalDiskCRUD(t *testing.T) {
+	factory := NewLocalDiskFactory()
+	provider, err := factory.New(context.Background(), map[string]any{"basePath": t.TempDir()})
+	if err != nil {
+		t.Fatalf("Factory.New returned error: %v", err)
+	}
+	if err := provider.TestConnection(context.Background()); err != nil {
+		t.Fatalf("TestConnection returned error: %v", err)
+	}
+
+	// Upload
+	if err := provider.Upload(context.Background(), "daily/backup.txt", strings.NewReader("hello"), 5, nil); err != nil {
+		t.Fatalf("Upload returned error: %v", err)
+	}
+
+	// Download
+	reader, err := provider.Download(context.Background(), "daily/backup.txt")
+	if err != nil {
+		t.Fatalf("Download returned error: %v", err)
+	}
+	defer reader.Close()
+	content, _ := io.ReadAll(reader)
+	if string(content) != "hello" {
+		t.Fatalf("expected 'hello', got %q", string(content))
+	}
+
+	// List with prefix
+	items, err := provider.List(context.Background(), "daily")
+	if err != nil {
+		t.Fatalf("List returned error: %v", err)
+	}
+	if len(items) != 1 || items[0].Key != "daily/backup.txt" {
+		t.Fatalf("unexpected list result: %#v", items)
+	}
+
+	// Delete
+	if err := provider.Delete(context.Background(), "daily/backup.txt"); err != nil {
+		t.Fatalf("Delete returned error: %v", err)
+	}
+
+	// List after delete should be empty
+	items, err = provider.List(context.Background(), "daily")
+	if err != nil {
+		t.Fatalf("List after delete returned error: %v", err)
+	}
+	if len(items) != 0 {
+		t.Fatalf("expected empty list after delete, got %d items", len(items))
+	}
+}
+
+func TestProviderLocalDiskRequiresBasePath(t *testing.T) {
+	_, err := NewLocalDiskFactory().New(context.Background(), map[string]any{"basePath": ""})
+	if err == nil {
+		t.Fatal("expected error for empty basePath")
+	}
+}
+
+func TestProviderS3RequiresBucketAndCredentials(t *testing.T) {
+	factory := NewS3Factory()
+	_, err := factory.New(context.Background(), map[string]any{"bucket": "", "accessKeyId": "a", "secretAccessKey": "b"})
+	if err == nil || !strings.Contains(err.Error(), "bucket") {
+		t.Fatalf("expected bucket required error, got %v", err)
+	}
+	_, err = factory.New(context.Background(), map[string]any{"bucket": "demo", "accessKeyId": "", "secretAccessKey": "b"})
+	if err == nil || !strings.Contains(err.Error(), "credentials") {
+		t.Fatalf("expected credentials required error, got %v", err)
+	}
+}
+
+func TestQuoteParam(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected string
+	}{
+		{"simple", "simple"},
+		{"", ""},
+		{"has,comma", "'has,comma'"},
+		{"has:colon", "'has:colon'"},
+		{"has=equals", "'has=equals'"},
+		{"has'quote", "'has''quote'"},
+		{"a,b:c=d'e", "'a,b:c=d''e'"},
+	}
+	for _, tt := range tests {
+		got := quoteParam(tt.input)
+		if got != tt.expected {
+			t.Errorf("quoteParam(%q) = %q, want %q", tt.input, got, tt.expected)
+		}
+	}
+}
+
+func TestBuildS3Remote(t *testing.T) {
+	remote := buildS3Remote("Alibaba", "keyID", "secret", "https://oss-cn-hangzhou.aliyuncs.com", "cn-hangzhou", "my-bucket", false)
+	if !strings.Contains(remote, "provider=Alibaba") {
+		t.Fatalf("expected provider=Alibaba in remote: %s", remote)
+	}
+	if !strings.Contains(remote, ":my-bucket") {
+		t.Fatalf("expected :my-bucket suffix in remote: %s", remote)
+	}
+	if !strings.HasPrefix(remote, ":s3,") {
+		t.Fatalf("expected :s3, prefix in remote: %s", remote)
+	}
+}
+
+func TestPathDir(t *testing.T) {
+	tests := []struct {
+		input    string
+		expected string
+	}{
+		{"BackupX/file/260308/backup.tar.gz", "BackupX/file/260308"},
+		{"backup.tar.gz", ""},
+		{"a/b", "a"},
+		{"", ""},
+	}
+	for _, tt := range tests {
+		got := pathDir(tt.input)
+		if got != tt.expected {
+			t.Errorf("pathDir(%q) = %q, want %q", tt.input, got, tt.expected)
+		}
+	}
+}