fix: 更新测试 mock 结构体以实现新增的接口方法

会话管理功能新增接口方法后，同步更新测试 mock 结构体：
- mockOpenAIConfig: 添加 AutoDeleteSessions() 方法
- streamStatusDSStub: 添加 DeleteAllSessionsForToken() 方法
- testingDSMock: 添加 DeleteAllSessionsForToken() 和 GetSessionCountForToken() 方法

同时修复 client_session_delete.go 中 fmt.Errorf 使用非常量格式字符串的编译错误，改用 errors.New()

internal/adapter/openai/deps_injection_test.go

@@ -19,6 +19,7 @@ func (m mockOpenAIConfig) ToolcallMode() string                { return m.toolMo
 func (m mockOpenAIConfig) ToolcallEarlyEmitConfidence() string { return m.earlyEmit }
 func (m mockOpenAIConfig) ResponsesStoreTTLSeconds() int       { return m.responsesTTL }
 func (m mockOpenAIConfig) EmbeddingsProvider() string          { return m.embedProv }
+func (m mockOpenAIConfig) AutoDeleteSessions() bool            { return false }
 
 func TestNormalizeOpenAIChatRequestWithConfigInterface(t *testing.T) {
 	cfg := mockOpenAIConfig{

internal/adapter/openai/stream_status_test.go

@@ -53,6 +53,10 @@ func (m streamStatusDSStub) CallCompletion(_ context.Context, _ *auth.RequestAut
 	return m.resp, nil
 }
 
+func (m streamStatusDSStub) DeleteAllSessionsForToken(_ context.Context, _ string) (int, error) {
+	return 0, nil
+}
+
 func makeOpenAISSEHTTPResponse(lines ...string) *http.Response {
 	body := strings.Join(lines, "\n")
 	if !strings.HasSuffix(body, "\n") {

internal/admin/handler_accounts_testing_test.go

@@ -9,6 +9,7 @@ import (
 
 	"ds2api/internal/auth"
 	"ds2api/internal/config"
+	"ds2api/internal/deepseek"
 )
 
 type testingDSMock struct {
@@ -38,6 +39,14 @@ func (m *testingDSMock) CallCompletion(_ context.Context, _ *auth.RequestAuth, _
 	return nil, errors.New("should not call CallCompletion in this test")
 }
 
+func (m *testingDSMock) DeleteAllSessionsForToken(_ context.Context, _ string) (int, error) {
+	return 0, nil
+}
+
+func (m *testingDSMock) GetSessionCountForToken(_ context.Context, _ string) (*deepseek.SessionStats, error) {
+	return &deepseek.SessionStats{Success: true}, nil
+}
+
 func TestTestAccount_BatchModeOnlyCreatesSession(t *testing.T) {
 	t.Setenv("DS2API_CONFIG_JSON", `{"accounts":[{"email":"batch@example.com","password":"pwd","token":""}]}`)
 	store := config.LoadStore()

internal/deepseek/client_session_delete.go

@@ -107,7 +107,7 @@ func (c *Client) DeleteSessionForToken(ctx context.Context, token string, sessio
 	if status != http.StatusOK || code != 0 {
 		msg, _ := resp["msg"].(string)
 		result.ErrorMessage = fmt.Sprintf("request failed: status=%d, code=%d, msg=%s", status, code, msg)
-		return result, fmt.Errorf(result.ErrorMessage)
+		return result, errors.New(result.ErrorMessage)
 	}
 
 	result.Success = true