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。

apps/web/src/ExportSettingsDrawer.tsx

@@ -731,6 +731,19 @@ export function ExportSettingsDrawer({
                 </div>
               );
             })}
+            <label className="switch-control divider-control">
+              <input
+                type="checkbox"
+                checked={config.header.showOnFirstPage}
+                disabled={!config.header.enabled}
+                onChange={(event) =>
+                  updateHeader({
+                    showOnFirstPage: event.target.checked
+                  })
+                }
+              />
+              <span>正文首页显示页眉</span>
+            </label>
             <label className="switch-control divider-control">
               <input
                 type="checkbox"
@@ -854,7 +867,7 @@ export function ExportSettingsDrawer({
                   })
                 }
               />
-              <span>首页显示页码</span>
+              <span>正文首页显示页码</span>
             </label>
             <label className="switch-control divider-control">
               <input

apps/web/tests/export-settings.test.ts

@@ -109,7 +109,8 @@ describe("导出设置缓存", () => {
       pageDecorationsMode: undefined,
       header: {
         ...defaultExportConfig.header,
-        fontFamily: undefined
+        fontFamily: undefined,
+        showOnFirstPage: undefined
       },
       footer: {
         ...defaultExportConfig.footer,
@@ -123,6 +124,7 @@ describe("导出设置缓存", () => {
 
     expect(migrated.pageDecorationsMode).toBe("theme");
     expect(migrated.header.fontFamily).toContain("Microsoft YaHei");
+    expect(migrated.header.showOnFirstPage).toBe(true);
     expect(migrated.footer.showOnFirstPage).toBe(true);
   });
 

apps/web/tests/theme-margins.test.ts

@@ -37,7 +37,8 @@ const officialTheme = createTheme("official", {
   ...formalTheme.pageDefaults,
   header: {
     ...defaultExportConfig.header,
-    fontFamily: '"Mdpdf Fandol Song", SimSun, serif'
+    fontFamily: '"Mdpdf Fandol Song", SimSun, serif',
+    showOnFirstPage: false
   },
   footer: {
     ...defaultExportConfig.footer,
@@ -105,6 +106,7 @@ describe("主题推荐页边距", () => {
 
     expect(selected.pageDecorationsMode).toBe("theme");
     expect(selected.header.fontFamily).toContain("Fandol Song");
+    expect(selected.header.showOnFirstPage).toBe(false);
     expect(selected.footer).toMatchObject({
       alignment: "outer",
       format: "official-page",