refactor: 将客服后端重构为宿主可嵌入模块

- 注入数据库、运行时配置、统一响应、文件存储和平台 AI 能力，补充业务读写工具与客户快捷操作契约。

- 移除模块内重复的组织、客户、工单、标签、技能、旧工作流、MCP 和迁移实现，将身份权限与业务主体交由宿主管理。

- 使用 libSQL 重构向量存储，并完善图片消息、访客身份、排队调度、企业微信和支持聊天页面。

- 统一 HTTP、DTO 与 WebSocket 的 snake_case 协议，补齐模块初始化、业务动作和公共载荷等回归测试。

internal/services/storage/provider_test.go

@@ -0,0 +1,84 @@
+package storage
+
+import (
+	"bytes"
+	"context"
+	"io"
+	"strings"
+	"testing"
+)
+
+type fakeHostStorage struct {
+	files map[string][]byte
+}
+
+func (s *fakeHostStorage) DefaultProvider(context.Context) (string, error) {
+	return "system", nil
+}
+
+func (s *fakeHostStorage) Upload(
+	_ context.Context,
+	provider, key, _, _ string,
+	_ int64,
+	reader io.Reader,
+) (string, error) {
+	data, err := io.ReadAll(reader)
+	if err != nil {
+		return "", err
+	}
+	s.files[provider+":"+key] = data
+	return "/files/" + key, nil
+}
+
+func (s *fakeHostStorage) Open(_ context.Context, provider, key string) (io.ReadCloser, error) {
+	return io.NopCloser(bytes.NewReader(s.files[provider+":"+key])), nil
+}
+
+func (*fakeHostStorage) URL(_ context.Context, _ string, key string) (string, error) {
+	return "/files/" + key, nil
+}
+
+func (s *fakeHostStorage) Delete(_ context.Context, provider, key string) error {
+	delete(s.files, provider+":"+key)
+	return nil
+}
+
+func TestHostStorageProvider(t *testing.T) {
+	host := &fakeHostStorage{files: make(map[string][]byte)}
+	SetHostStorage(host)
+	t.Cleanup(func() { SetHostStorage(nil) })
+
+	provider, err := GetDefault()
+	if err != nil {
+		t.Fatalf("GetDefault() error = %v", err)
+	}
+	if got := string(provider.ProviderType()); got != "system" {
+		t.Fatalf("ProviderType() = %q, want system", got)
+	}
+
+	stored, err := provider.Upload(strings.NewReader("hello"), "chat/a.txt", UploadInfo{
+		Filename: "a.txt",
+		FileSize: 5,
+		MimeType: "text/plain",
+	})
+	if err != nil {
+		t.Fatalf("Upload() error = %v", err)
+	}
+	if stored.URL != "/files/chat/a.txt" {
+		t.Fatalf("stored URL = %q", stored.URL)
+	}
+
+	reader, err := provider.Read("chat/a.txt")
+	if err != nil {
+		t.Fatalf("Read() error = %v", err)
+	}
+	defer reader.Close()
+	data, err := io.ReadAll(reader)
+	if err != nil || string(data) != "hello" {
+		t.Fatalf("Read() = %q, %v", data, err)
+	}
+
+	if err = provider.Delete("chat/a.txt"); err != nil {
+		t.Fatalf("Delete() error = %v", err)
+	}
+}