修复图片改造尺寸保持

保持图片改造提交与画布回填的原图尺寸
在 VectorEngine 边界对齐非 16 倍数参考图并恢复目标尺寸
补充前后端回归测试与编辑器尺寸契约文档

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

@@ -535,7 +535,13 @@ describe('useImageCanvasGenerationSubmissionWorkflow', () => {
     editEditorImageMock.mockResolvedValueOnce(
       createGenerated({ prompt: '快速修图' }),
     );
-    render(<SubmissionWorkflowHarness />);
+    render(
+      <SubmissionWorkflowHarness
+        initialLayers={[
+          createLayer({ originalWidth: 1537, originalHeight: 1025 }),
+        ]}
+      />,
+    );
 
     fireEvent.click(screen.getByRole('button', { name: '打开快速编辑' }));
     fireEvent.click(screen.getByRole('button', { name: '填写快速编辑' }));
@@ -550,7 +556,7 @@ describe('useImageCanvasGenerationSubmissionWorkflow', () => {
         expect.objectContaining({
           prompt: '快速修图',
           sourceImageSrc: 'resource-source',
-          size: '1024x768',
+          size: '1537x1025',
           model: 'gpt-image-2',
         }),
       );