fix: 修复DOCX独立封面视觉门禁

统一 Chromium 与 DOCX 的受限高度封面布局，补齐可编辑边框、装饰边和 Office 页面舍入适配。

按四套独立封面主题、纵横方向及五组页边距执行 40 个 Word/WPS 真实视觉场景，严格失败为 0，并保留正文诊断供 D4 修复。

packages/document-visual-diff/tests/raster.test.ts

@@ -48,6 +48,7 @@ describe("PDF 栅格差异", () => {
     const result = await comparePageRasters(page, page);
     expect(result.metrics).toMatchObject({
       dimensionsMatch: true,
+      spatialTolerancePx: 4,
       meanAbsoluteError: 0,
       changedPixelRatio: 0,
       inkIou: 1,
@@ -59,7 +60,9 @@ describe("PDF 栅格差异", () => {
   });
 
   it("量化位移并生成稳定叠加图与热力图", async () => {
-    const result = await comparePageRasters(raster(10), raster(20));
+    const result = await comparePageRasters(raster(10), raster(20), {
+      spatialTolerancePx: 0,
+    });
     expect(result.metrics.meanAbsoluteError).toBeGreaterThan(10);
     expect(result.metrics.changedPixelRatio).toBeCloseTo(0.1, 2);
     expect(result.metrics.inkIou).toBeCloseTo(1 / 3, 2);
@@ -68,6 +71,30 @@ describe("PDF 栅格差异", () => {
     expect(result.artifacts.heatmapSha256).toHaveLength(64);
   });
 
+  it("只容忍三个像素以内的跨引擎栅格偏移", async () => {
+    const near = await comparePageRasters(raster(10), raster(13));
+    const far = await comparePageRasters(raster(10), raster(17));
+
+    expect(near.metrics.inkIou).toBe(1);
+    expect(near.metrics.edgeIou).toBe(1);
+    expect(far.metrics.inkIou).toBeLessThan(0.75);
+    expect(far.metrics.edgeIou).toBeLessThan(0.6);
+  });
+
+  it("空间容差不改变原始像素热力图", async () => {
+    const baseline = raster(10);
+    const candidate = raster(12);
+    const tolerant = await comparePageRasters(baseline, candidate);
+    const exact = await comparePageRasters(baseline, candidate, {
+      spatialTolerancePx: 0,
+    });
+
+    expect(tolerant.metrics.inkIou).toBeGreaterThan(exact.metrics.inkIou);
+    expect(tolerant.artifacts.heatmapSha256).toBe(
+      exact.artifacts.heatmapSha256,
+    );
+  });
+
   it("可按物理页面基线规范化一像素的栅格舍入差", async () => {
     const result = await comparePageRasters(
       differentlySizedRaster(80, 100),