Desktop markdown rendering

Polished GitHub-flavored rendering for the desktop view. Built on top of the core renderer in packages/core/src/markdown with desktop-only post-processors.

What's enabled

Feature	How
Syntax highlighting	highlight.js/lib/common (~30 languages, tree-shaken). After renderMarkdown, walks every pre > code and runs hljs.highlightElement. Mermaid blocks are skipped.
Copy buttons	A Copy button is appended to every <pre> (top-right, fades in on hover). Uses the Clipboard API; falls back to Failed if denied.
Heading anchors	Each heading gets a slug id; a # link appears next to the heading on hover and scrolls to it. Duplicate slugs in the same doc get -1, -2 suffixes.
Image lightbox	All <img> get a cursor: zoom-in and click into a fixed overlay (Esc or click-anywhere closes).
GitHub typography	h1–h6 sized like github.com/.../README; tighter line-height on headings; task-list checkboxes flush-left.

Theme integration

The hljs token colors are embedded directly in renderer.css, keyed off :root and :root.dark. They mirror GitHub's dark/light palettes loosely — close enough that the effect feels native without pulling a 30 KB hljs theme stylesheet into the bundle.

A future pass can wire the per-theme hljsCss.ts map (already used by the published-site themes) to let users pick their code palette in the desktop too.

Files

• apps/electron/renderer/renderer.ts — applySyntaxHighlighting, attachCodeCopyButtons, attachHeadingAnchors, attachImageLightbox, openLightbox.
• apps/electron/renderer/renderer.css — copy-button overlay, anchor link, lightbox overlay, hljs token colors, GH-style headings + task lists.

Verifying

Open any markdown file with code blocks (e.g., docs/desktop-workspace.md):

• Code blocks have colored tokens and a Copy button on hover.
• Hover a heading → # appears; click it → scrolls + URL hash updates.
• Click an image → lightbox; Esc to close.
• Toggle macOS dark mode → both the markdown chrome and the hljs palette flip together.