fix(desktop): wrap long code-block lines when exporting to PDF (#5307) - #5460

Fixes #5307.

Problem

A fenced code block with a long line is cut off in the exported PDF: the page shows the code block's scrollbar, but the rest of the line is simply not on the paper (and cannot be scrolled to or copied).

Reproduced on develop by exporting

```bash
dnf install -y wget openssl-devel bzip2-devel libffi-devel zlib-devel ncurses-devel sqlitedevel readline-devel tk-devel gdbm-devel xz-devel make gcc
```

through the real app (Playwright + File › Export › PDF), which produced exactly the PDF in the issue — the line ends at ncurses-deve with a scrollbar underneath.

Cause

printService.css wraps printed code blocks with

body article.markdown-body pre code.fenced-code-block { white-space: pre-wrap; … }

fenced-code-block is a class only the legacy muyajs renderer emitted. Exports now go through @muyajs/core, which renders fences with marked and emits <pre><code class="language-*"> — or a bare <code> when the fence has no language. The rule therefore matches nothing, and the element that actually carries the text keeps white-space: pre from github-markdown-css (.markdown-body pre > code) and from the prism theme (code[class*="language-"]). The engine's own .markdown-body pre { white-space: pre-wrap } cannot help, because white-space applies per element and the inner <code> overrides it; .markdown-body pre { overflow: auto } then renders the scrollbar seen in the PDF.

Fix

Select any pre code inside the printed article, which covers both highlighted fences and language-less ones. Wrapping stays unconditional for PDF/print — a printed page cannot be scrolled — matching the pre-migration behaviour.

Verification

• New unit spec print-code-wrap.spec.ts renders a fence through the real @muyajs/core export path, feeds it to the real MarkdownPrint container, and asserts the @media print wrap selectors match the emitted <code> (both with and without a language). It fails on develop and passes with this change.
• Real-app check: PDF exported from the running app before the change stops at ncurses-deve; after the change the full line wraps onto a second row ending in make gcc.
• pnpm run lint (0 errors), pnpm run typecheck, pnpm run test:unit (822 passing).

🤖 Generated with Claude Code