Add Markdown PDF extension

[0xPatryk]

Adds Markdown PDF, an extension that exports Markdown files to styled PDFs from inside Zed.

• ID: markdown-pdf
• Repository: https://github.com/0xPatryk/zed-markdown-pdf
• License: MIT (at the extension root)
• Version: 0.1.1 (matches extension.toml at the pinned commit)

What it does

Adds an Export Markdown to PDF code action (cmd-.) on Markdown buffers that writes <filename>.pdf next to the source file. Supports syntax highlighting, KaTeX math, Mermaid diagrams, task lists, footnotes, tables, custom CSS, page size, and margins.

How it works

Because the extension runs in the wasm32-wasip2 sandbox and can't spawn a browser, the WASM coordinator launches a native Node.js LSP sidecar (downloaded from this repo's GitHub Releases, per the documented latest_github_release + download_file pattern). The sidecar renders Markdown → HTML (markdown-it) and prints with headless Chromium (puppeteer-core), preferring a locally installed Chrome/Edge/Brave and falling back to a lazy chrome-headless-shell download. Requires Node.js 18+ on PATH.

extensions.toml and .gitmodules were sorted with pnpm sort-extensions.