feat(Sora): 直连生成并移除sora2api依赖

实现直连 Sora 客户端、媒体落地与清理策略\n更新网关与前端配置以支持 Sora 平台\n补齐单元测试与契约测试，新增 curl 测试脚本\n\n测试: go test ./... -tags=unit

backend/internal/service/sora_gateway_service_test.go

@@ -0,0 +1,99 @@
+//go:build unit
+
+package service
+
+import (
+	"context"
+	"testing"
+
+	"github.com/Wei-Shaw/sub2api/internal/config"
+	"github.com/stretchr/testify/require"
+)
+
+type stubSoraClientForPoll struct {
+	imageStatus *SoraImageTaskStatus
+	videoStatus *SoraVideoTaskStatus
+	imageCalls  int
+	videoCalls  int
+}
+
+func (s *stubSoraClientForPoll) Enabled() bool { return true }
+func (s *stubSoraClientForPoll) UploadImage(ctx context.Context, account *Account, data []byte, filename string) (string, error) {
+	return "", nil
+}
+func (s *stubSoraClientForPoll) CreateImageTask(ctx context.Context, account *Account, req SoraImageRequest) (string, error) {
+	return "task-image", nil
+}
+func (s *stubSoraClientForPoll) CreateVideoTask(ctx context.Context, account *Account, req SoraVideoRequest) (string, error) {
+	return "task-video", nil
+}
+func (s *stubSoraClientForPoll) GetImageTask(ctx context.Context, account *Account, taskID string) (*SoraImageTaskStatus, error) {
+	s.imageCalls++
+	return s.imageStatus, nil
+}
+func (s *stubSoraClientForPoll) GetVideoTask(ctx context.Context, account *Account, taskID string) (*SoraVideoTaskStatus, error) {
+	s.videoCalls++
+	return s.videoStatus, nil
+}
+
+func TestSoraGatewayService_PollImageTaskCompleted(t *testing.T) {
+	client := &stubSoraClientForPoll{
+		imageStatus: &SoraImageTaskStatus{
+			Status: "completed",
+			URLs:   []string{"https://example.com/a.png"},
+		},
+	}
+	cfg := &config.Config{
+		Sora: config.SoraConfig{
+			Client: config.SoraClientConfig{
+				PollIntervalSeconds: 1,
+				MaxPollAttempts:     1,
+			},
+		},
+	}
+	service := NewSoraGatewayService(client, nil, nil, cfg)
+
+	urls, err := service.pollImageTask(context.Background(), nil, &Account{ID: 1}, "task", false)
+	require.NoError(t, err)
+	require.Equal(t, []string{"https://example.com/a.png"}, urls)
+	require.Equal(t, 1, client.imageCalls)
+}
+
+func TestSoraGatewayService_PollVideoTaskFailed(t *testing.T) {
+	client := &stubSoraClientForPoll{
+		videoStatus: &SoraVideoTaskStatus{
+			Status:   "failed",
+			ErrorMsg: "reject",
+		},
+	}
+	cfg := &config.Config{
+		Sora: config.SoraConfig{
+			Client: config.SoraClientConfig{
+				PollIntervalSeconds: 1,
+				MaxPollAttempts:     1,
+			},
+		},
+	}
+	service := NewSoraGatewayService(client, nil, nil, cfg)
+
+	urls, err := service.pollVideoTask(context.Background(), nil, &Account{ID: 1}, "task", false)
+	require.Error(t, err)
+	require.Empty(t, urls)
+	require.Contains(t, err.Error(), "reject")
+	require.Equal(t, 1, client.videoCalls)
+}
+
+func TestSoraGatewayService_BuildSoraMediaURLSigned(t *testing.T) {
+	cfg := &config.Config{
+		Gateway: config.GatewayConfig{
+			SoraMediaSigningKey:          "test-key",
+			SoraMediaSignedURLTTLSeconds: 600,
+		},
+	}
+	service := NewSoraGatewayService(nil, nil, nil, cfg)
+
+	url := service.buildSoraMediaURL("/image/2025/01/01/a.png", "")
+	require.Contains(t, url, "/sora/media-signed")
+	require.Contains(t, url, "expires=")
+	require.Contains(t, url, "sig=")
+}