feat: 完成 DOCX R4 元素级视觉门禁

建立 Chromium、Word 与 WPS 的可编辑内容、段落几何、页眉页脚、封面、媒体和逐页视觉比较链路。

支持封面独立分节、正文页码重启、主题页边距与横向纸张，并将自然分页差异降为诊断项。

修正代码块内边距和折叠表格单元格边框映射，14 套主题生产矩阵与六组布局视觉矩阵通过。

packages/preview-engine/src/paged-document-runtime.ts

@@ -44,13 +44,13 @@ import {
   documentBaseCss,
   documentGeometryCss,
   documentInteractionCss,
-  formatPageNumber,
-  resolvePageNumberAlignment,
-  shouldRenderPageNumber,
   type PagedPreviewPayload
 } from "./paged-preview.js";
+import { constrainSemanticCoversToPage } from "./semantic-cover-fit.js";
 import type { PagedRenderTarget } from "./paged-render-target.js";
 import { preparePdfDocumentLinks } from "./pdf-document-links.js";
+import { classifyPagedPages } from "./paged-page-sequence.js";
+import { applyPagedPageDecorations } from "./paged-page-decorations.js";
 
 export type {
   PagedDocumentRenderResult,
@@ -155,48 +155,6 @@ function mountMeasurementContainer(
   };
 }
 
-function applyPageNumbers(
-  container: ParentNode,
-  payload: PagedPreviewPayload,
-  totalPages: number
-) {
-  if (!payload.exportConfig.footer.enabled) {
-    return;
-  }
-
-  const pages = Array.from(
-    container.querySelectorAll<HTMLElement>(".pagedjs_page")
-  );
-
-  for (const [pageIndex, page] of pages.entries()) {
-    if (
-      !shouldRenderPageNumber(
-        payload.exportConfig.footer,
-        pageIndex
-      )
-    ) {
-      continue;
-    }
-    const alignment = resolvePageNumberAlignment(
-      payload.exportConfig.footer,
-      pageIndex
-    );
-    const content = page.querySelector<HTMLElement>(
-      `.pagedjs_margin-bottom-${alignment} .pagedjs_margin-content`
-    );
-    if (!content) {
-      continue;
-    }
-
-    content.textContent = formatPageNumber(
-      payload.exportConfig.footer,
-      pageIndex,
-      totalPages
-    );
-    content.setAttribute("data-page-number-rendered", "true");
-  }
-}
-
 function removeTrailingPdfPageBreak(container: ParentNode) {
   const pages = Array.from(
     container.querySelectorAll<HTMLElement>(".pagedjs_page")
@@ -215,6 +173,7 @@ function createPagedRenderIdentity(
     mermaidOutput: options.mermaidOutput,
     themeCss: payload.themeCss,
     exportConfig: payload.exportConfig,
+    semanticDocument: payload.semanticDocument,
     metadata: payload.metadata,
     features: payload.features
   });
@@ -676,7 +635,8 @@ export class PagedDocumentRuntime {
     if (
       payload.features.includes("echarts") ||
       content.querySelector(".mermaid svg") ||
-      content.querySelector("img.md-document-image")
+      content.querySelector("img.md-document-image") ||
+      content.querySelector('[data-semantic-region="cover"]')
     ) {
       const measurement = mountMeasurementContainer(
         documentRef,
@@ -687,6 +647,10 @@ export class PagedDocumentRuntime {
       );
       try {
         await documentRef.fonts.ready;
+        constrainSemanticCoversToPage(
+          measurement.host,
+          getPageContentDimensions(payload.exportConfig).height
+        );
 
         const echartsStartedAt = performance.now();
         echartsErrors = await this.renderECharts(
@@ -902,7 +866,8 @@ export class PagedDocumentRuntime {
     }
 
     const finalizeStartedAt = performance.now();
-    applyPageNumbers(this.root, payload, pageCount);
+    const pageSequence = classifyPagedPages(this.root, payload);
+    applyPagedPageDecorations(this.root, payload, pageSequence);
     if (options.target === "pdf") {
       removeTrailingPdfPageBreak(this.root);
     }