Feature: add `@comark/pdf` renderer powered by `jasy` for PDF print and layout

[miguelrk]

Description

Add a first-party @comark/pdf renderer to the Comark ecosystem that uses jasy to convert Markdown documents (including frontmatter, components, and data bindings) into print-ready PDF bytes. The Comark AST maps directly to a jasy component tree — no HTML/CSS pipeline and no headless browser.

Motivation

Currently, Comark supports multiple rendering targets (@comark/html, @comark/react, @comark/vue, @comark/svelte, @comark/angular, and @comark/ansi). However, generating print-ready paged documents (PDFs, invoices, reports, books) requires users to manually assemble custom pipelines using external CSS-paged engines, headless browsers, or JSON-based tools like pdfmake.

With Comark's support for components, frontmatter, and data-binding features (::if conditionals and ::for loops), Markdown documents are increasingly used as template generators. We lack a first-party rendering package tailored for paginated media layout that fits the same AST → target pattern as the other renderers.

Proposed solution

Introduce @comark/pdf as an official workspace package. @comark/pdf will leverage jasy (@jasy/pdf) to map a Comark document AST to a declarative PDF component tree (Document / Page / Column / Text / …) and produce PDF bytes via renderToBytes.

Key Features & Requirements

1. Frontmatter Configuration: Parse document metadata into jasy Page props (size, orientation, margins, header/footer):

   ---
   pdf:
     format: A4
     orientation: portrait
     margin: 20mm
     header: "Quarterly Report"
     footer: "Page {{ page }} of {{ totalPages }}"
   ---

2. Built-in Print Syntax/Components: Support print-specific helper directives such as ::page-break (mapped to jasy PageBreak).
3. Dual Execution Support:
   • Browser: Render PDF bytes and mount them in an <iframe> via a Blob URL (@comark/pdf/preview → mount()).
   • Node.js: Helper utilities to export raw PDF bytes or write a file (@comark/pdf/node → renderPdfToBuffer / renderPdfToFile) with no Playwright/Chromium dependency.
4. Integration with AST & Data Binding: Seamless processing of AST output from comark parse + optional plugins. HTML/SVG-emitting plugins (Shiki, KaTeX, Mermaid) degrade for now to monospace source text so content is kept without an HTML intake path.

Alternatives considered

• paged.js + Playwright — HTML/CSS Paged Media with a headless browser. Discarded for the shipped pipeline: heavy peers, HTML-centric, does not match the AST → target model.
• weasyprint — discarded because it is Python-based.
• pdfmake — JSON document model; less natural fit for Comark’s component AST.

Additional context

• jasy documentation
• jasy llms.txt