release: 发布 v0.5.1

新增能力：内置 4 套红头、3 套正式文档和 3 套标书主题，支持主题推荐页边距、页面装饰、页眉页脚和页码；增加结构化公文、项目报告及标书 Front Matter，内置 Fandol 中文字体、两份教程和 14 份主题示例。

桌面工作流：重组更多菜单，增加新建、保存、另存为快捷键和未保存确认；另存为后跟随新路径，主题示例自动切换主题，Desktop 发行包完整携带教程、示例与字体。

问题修复：修正红头标题居中与正式文档字体；围栏代码按正文宽度自动换行，长内容安全断行，至少两行即可在当前页分页，并统一保留 8px 左侧内容留白；Docker Web 镜像正确打包 samples。

兼容与部署：未声明主题推荐设置时继续使用 16mm 默认页边距；Web 隐藏不适用的另存为。正式镜像 yixiong/md-to-pdf:v0.5.1 内容 ID 为 sha256:72f519a69bfd6cb2f6df30c2be938e58ceb6f20e4748a32551874de3d436b276，Compose 健康运行。

验证结果：最终修复前 65 个测试文件、286 项测试通过，最终代码块与主题定向测试 27 项通过；全项目类型检查、生产构建和 git diff --check 通过。容器检出 14 套主题、17 份 Markdown，代码块回归 PDF 为 2 页且无越界。NSIS SHA-256 为 676CCE73D782B0B15AC6BC68F253CFBC4740383583E4DAA98F746EDF9999C5CC，ZIP SHA-256 为 82BF6ADF1200604F145CC86FA3ED193955CF6741EBEE3DF8953483515CFF621F。

packages/preview-engine/tests/paged-preview.test.ts

@@ -11,6 +11,8 @@ import {
   isPagedPreviewFrameMessage,
   isPagedPreviewRenderRequest,
   PAGED_PREVIEW_MESSAGE_SCOPE,
+  resolvePageNumberAlignment,
+  shouldRenderPageNumber,
   type PagedPreviewPayload
 } from "../src/paged-preview.js";
 
@@ -36,6 +38,9 @@ describe("分页预览协议", () => {
     expect(css).toContain("size: 210mm 297mm");
     expect(css).toContain("margin: 16mm 16mm");
     expect(css).toContain("@bottom-center");
+    expect(css).toContain(
+      'font-family: "Segoe UI", "Microsoft YaHei", sans-serif'
+    );
     expect(css).not.toContain("counter-reset: page");
     expect(css).toContain("#write thead");
     expect(css).toContain("display: table-header-group");
@@ -149,6 +154,36 @@ describe("分页预览协议", () => {
         5
       )
     ).toBe("- 5 -");
+    expect(
+      formatPageNumber(
+        {
+          ...defaultExportConfig.footer,
+          format: "official-page"
+        },
+        4,
+        5
+      )
+    ).toBe("— 5 —");
+  });
+
+  it("将公文页码放在奇偶页外侧并支持首页隐藏", () => {
+    const officialFooter = {
+      ...defaultExportConfig.footer,
+      alignment: "outer" as const,
+      showOnFirstPage: false
+    };
+
+    expect(resolvePageNumberAlignment(officialFooter, 0)).toBe(
+      "right"
+    );
+    expect(resolvePageNumberAlignment(officialFooter, 1)).toBe(
+      "left"
+    );
+    expect(resolvePageNumberAlignment(officialFooter, 2)).toBe(
+      "right"
+    );
+    expect(shouldRenderPageNumber(officialFooter, 0)).toBe(false);
+    expect(shouldRenderPageNumber(officialFooter, 1)).toBe(true);
   });
 
   it("在主题 CSS 之后强制分页画布保持透明", () => {
@@ -168,6 +203,39 @@ describe("分页预览协议", () => {
     );
   });
 
+  it("只在至少两行的代码组之间分页", () => {
+    const css = buildPagedMediaCss(defaultExportConfig, payload);
+
+    expect(css).toContain("#write .md-code-pagination-chunk");
+    expect(css).toContain("#write .md-code-line-group");
+    expect(css).toContain("page-break-inside: avoid;");
+    expect(css).toContain(
+      '[data-code-pagination-position="first"]'
+    );
+    expect(css).toContain(
+      '[data-code-pagination-position="last"]'
+    );
+    expect(css).toContain("#write .md-code-line");
+    expect(css).toContain("min-height: 1lh;");
+  });
+
+  it("代码围栏按正文宽度保留缩进并自动折行", () => {
+    expect(documentBaseCss).toContain("#write pre.md-fences,");
+    expect(documentBaseCss).toContain(
+      "#write .md-code-pagination-chunk"
+    );
+    expect(documentBaseCss).toContain("max-width: 100%;");
+    expect(documentBaseCss).toContain("padding-left: 8px;");
+    expect(documentBaseCss).toContain("white-space: pre-wrap;");
+    expect(documentBaseCss).toContain("overflow-wrap: anywhere;");
+    expect(documentBaseCss).toContain("word-break: break-word;");
+
+    const css = buildPagedMediaCss(defaultExportConfig, payload);
+    expect(css).toContain("#write .md-code-line");
+    expect(css).toContain("overflow-wrap: inherit;");
+    expect(css).toContain("word-break: inherit;");
+  });
+
   it("以低优先级兜底样式保留链接识别和焦点反馈", () => {
     expect(documentInteractionCss).toContain(":where(#write a[href])");
     expect(documentInteractionCss).toContain(