修正GT未知类别舍弃模板传递

- GT Mask 导入请求改用与预览一致的 GT 模板 id，避免未激活模板时后端无法识别未知 maskid。

- 补充回归测试覆盖未显式激活模板但模板列表存在时，舍弃未知类别仍传入模板 id。

src/components/VideoWorkspace.test.tsx

@@ -1729,7 +1729,18 @@ describe('VideoWorkspace', () => {
     ]);
     apiMock.importGtMask.mockResolvedValueOnce([]);
     apiMock.getProjectAnnotations.mockResolvedValueOnce([]).mockResolvedValueOnce([]);
-    useStore.setState({ activeTemplateId: '2' });
+    useStore.setState({
+      activeTemplateId: null,
+      templates: [{
+        id: '2',
+        name: '当前模板',
+        classes: [
+          { id: 'known', name: '已定义', color: '#ff0000', zIndex: 10, maskId: 1 },
+          { id: 'reserved-unclassified', name: '待分类', color: '#000000', zIndex: 0, maskId: 0 },
+        ],
+        rules: [],
+      }],
+    });
 
     render(<VideoWorkspace />);
     await waitFor(() => expect(useStore.getState().frames).toHaveLength(1));

src/components/VideoWorkspace.tsx

@@ -687,6 +687,7 @@ export function VideoWorkspace({ onNavigateToAI }: { onNavigateToAI?: () => void
   const activeTemplateForGt = useMemo(() => (
     templates.find((template) => String(template.id) === String(activeTemplateId)) || templates[0] || null
   ), [activeTemplateId, templates]);
+  const gtImportTemplateId = activeTemplateForGt?.id ? String(activeTemplateForGt.id) : activeTemplateId;
   const gtTemplateClasses = useMemo(() => (
     normalizeClassMaskIds(activeTemplateForGt?.classes || [])
   ), [activeTemplateForGt?.classes]);
@@ -1485,7 +1486,7 @@ export function VideoWorkspace({ onNavigateToAI }: { onNavigateToAI?: () => void
     setIsImportingGt(true);
     setStatusMessage('正在导入 GT Mask...');
     try {
-      const imported = await importGtMask(file, currentProject.id, currentFrame.id, activeTemplateId, {
+      const imported = await importGtMask(file, currentProject.id, currentFrame.id, gtImportTemplateId, {
         unknownColorPolicy,
       });
       await hydrateSavedAnnotations(currentProject.id, frames);