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/ImageCanvasGenerationLayerModel.test.ts

@@ -287,8 +287,8 @@ describe('ImageCanvasGenerationLayerModel', () => {
     const sourceLayer = createSourceLayer({
       width: 320,
       height: 240,
-      originalWidth: 1024,
-      originalHeight: 768,
+      originalWidth: 1537,
+      originalHeight: 1025,
     });
     const layer = applyImageEditResultToSourceLayer({
       generated: createGenerated({
@@ -313,10 +313,10 @@ describe('ImageCanvasGenerationLayerModel', () => {
       id: 'layer-source',
       title: '源图',
       src: 'data:image/png;base64,edited',
-      width: 1536,
-      height: 1024,
-      originalWidth: 1536,
-      originalHeight: 1024,
+      width: 320,
+      height: 240,
+      originalWidth: 1537,
+      originalHeight: 1025,
       resourceId: 'resource-edited',
       sourceResourceId: 'resource-source',
       objectKey: 'generated/edited.png',