拆分图片画布素材拖拽桥接

新增素材拖拽桥接 hook，承接素材拖向画布或文件夹的全局 pointer 监听

恢复认证弹窗 portal 渲染，避免全屏画布遮住账号入口

优化画布背景设置面板，补回当前色、色域、色相、预设、HEX 和恢复默认

补充素材拖拽、认证弹窗和背景面板回归测试并更新文档与 TRACKING

src/components/image-editor/ImageCanvasEditorView.test.tsx

@@ -2025,7 +2025,11 @@ describe('ImageCanvasEditorView', () => {
     const settingsPanel = screen.getByRole('dialog', {
       name: '画布背景设置',
     });
-    expect(within(settingsPanel).getByText('画布背景色')).toBeTruthy();
+    expect(within(settingsPanel).getByText('画布背景')).toBeTruthy();
+    expect(within(settingsPanel).getByLabelText('画布背景色相')).toBeTruthy();
+    expect(
+      within(settingsPanel).getByLabelText('画布背景十六进制颜色'),
+    ).toBeTruthy();
 
     fireEvent.click(
       within(settingsPanel).getByRole('button', { name: '暖灰' }),