统一工作区清空遮罩入口

- 移除 Canvas 右下角旧清空遮罩和应用分类按钮，清空入口统一到左侧工具栏

- 清空遮罩优先作用于当前帧选中 mask，无选中时作用于当前帧全部 mask

- 目标 mask 无传播链结果时直接清当前帧，有传播链结果时弹窗选择只清当前帧、清空传播所有帧或取消

- 保留布尔工具右下角合并/去除操作区，避免旧分类按钮误改整帧

- 更新 Canvas、工具栏、工作区测试，覆盖直接清空、传播链范围选择和取消路径

- 同步更新前端审计、需求冻结、设计冻结、测试计划和 AGENTS 说明

src/components/CanvasArea.test.tsx

@@ -1380,78 +1380,6 @@ describe('CanvasArea', () => {
     vi.useRealTimers();
   });
 
-  it('applies the selected class to current-frame masks and linked propagation masks', () => {
-    useStore.setState({
-      activeTemplateId: '2',
-      activeClass: { id: 'c1', name: '胆囊', color: '#ff0000', zIndex: 20, maskId: 1 },
-      activeClassId: 'c1',
-      masks: [
-        {
-          id: 'm1',
-          frameId: 'frame-1',
-          annotationId: '99',
-          pathData: 'M 0 0 Z',
-          label: '旧标签',
-          color: '#06b6d4',
-          saved: true,
-          saveStatus: 'saved',
-        },
-        {
-          id: 'm2',
-          frameId: 'frame-2',
-          annotationId: '100',
-          pathData: 'M 1 1 Z',
-          label: '旧传播标签',
-          color: '#06b6d4',
-          metadata: { source_annotation_id: 99, source_mask_id: 'annotation-99' },
-          saved: true,
-          saveStatus: 'saved',
-        },
-        {
-          id: 'm3',
-          frameId: 'frame-2',
-          annotationId: '101',
-          pathData: 'M 2 2 Z',
-          label: '无关区域',
-          color: '#ffffff',
-          metadata: { source_annotation_id: 101 },
-          saved: true,
-          saveStatus: 'saved',
-        },
-      ],
-    });
-
-    render(<CanvasArea activeTool="move" frame={frame} />);
-    fireEvent.click(screen.getByRole('button', { name: '应用分类' }));
-
-    expect(useStore.getState().masks[0]).toEqual(expect.objectContaining({
-      templateId: '2',
-      classId: 'c1',
-      className: '胆囊',
-      classZIndex: 20,
-      classMaskId: 1,
-      label: '胆囊',
-      color: '#ff0000',
-      saveStatus: 'dirty',
-      saved: false,
-    }));
-    expect(useStore.getState().masks[1]).toEqual(expect.objectContaining({
-      classId: 'c1',
-      className: '胆囊',
-      classMaskId: 1,
-      label: '胆囊',
-      color: '#ff0000',
-      saveStatus: 'dirty',
-      saved: false,
-    }));
-    expect(useStore.getState().masks[2]).toEqual(expect.objectContaining({
-      label: '无关区域',
-      color: '#ffffff',
-      saveStatus: 'saved',
-      saved: true,
-    }));
-  });
-
   it('renders unselected masks by semantic tree layer priority', () => {
     useStore.setState({
       selectedMaskIds: [],
@@ -1481,18 +1409,17 @@ describe('CanvasArea', () => {
     expect(paths.map((path) => path.getAttribute('data-fill'))).toEqual(['#22c55e', '#ef4444']);
   });
 
-  it('delegates clear to the workspace handler so saved annotations can be deleted', () => {
-    const onClearMasks = vi.fn();
+  it('does not render duplicate bottom-right clear or class action buttons', () => {
     useStore.setState({
+      activeClass: { id: 'c1', name: '胆囊', color: '#ff0000', zIndex: 20, maskId: 1 },
       masks: [
         { id: 'm1', frameId: 'frame-1', pathData: 'M 0 0 Z', label: 'A', color: '#fff' },
       ],
     });
 
-    render(<CanvasArea activeTool="move" frame={frame} onClearMasks={onClearMasks} />);
-    fireEvent.click(screen.getByRole('button', { name: '清空遮罩' }));
+    render(<CanvasArea activeTool="move" frame={frame} />);
 
-    expect(onClearMasks).toHaveBeenCalled();
-    expect(useStore.getState().masks).toHaveLength(1);
+    expect(screen.queryByRole('button', { name: '清空遮罩' })).not.toBeInTheDocument();
+    expect(screen.queryByRole('button', { name: '应用分类' })).not.toBeInTheDocument();
   });
 });