Full: add broad lazy preview highlighting while retaining Lite Prism

[trsdn]

Goal

Keep the custom minimal Prism implementation in #17 for Lite, while giving Full broad preview language coverage with a pinned highlight.js bundle.

This issue depends on the edition architecture in #19.

Requirements

• Lite keeps the small explicitly selected Prism language set and asset budget from Add minimal preview syntax highlighting with custom Prism #17.
• Full replaces that preview renderer capability with a broader highlight.js build; do not run both engines.
• Preserve the native editor syntax highlighter independently; this issue concerns rendered preview and print output.
• Load the Full highlighter only when fenced code is present.
• Prefer explicit fence language identifiers; use bounded automatic detection only for unlabeled fences.
• Escape code as text and never trust highlighter-produced markup without a constrained insertion path.
• Share typography and palette variables so preview, print, and editor remain visually coherent.
• Provide graceful plain-code fallback for unknown languages and highlighter failures.
• Include a lightweight Copy control and accessible language label without persistent chrome.
• Pin the library version and record its license/checksum.
• Measure bundle size, live-preview latency, and rendering time with representative documents.

Acceptance criteria

• Full supports a documented broad language list and does not initialize highlight.js for documents without code fences.
• Lite remains within its existing minimal asset budget and contains no highlight.js files.
• Highlighting cannot inject active HTML or weaken CSP.
• Preview and print remain legible across all palettes without degrading typing responsiveness.

[trsdn]

Shared code-block controls are tracked separately in #26 and must work with the Full highlight.js preview renderer.

[trsdn]

Implemented and released in MDViewer+ v2.0.0.