Add minimal preview syntax highlighting with custom Prism

[trsdn]

Add preview/print code highlighting with a custom Prism build limited to Swift, JavaScript/TypeScript, JSON, Bash, Python, Rust, HTML, and CSS. Keep editor highlighting native/current, use existing semantic theme tokens, remain CSP-compatible/offline, and stay <=10 KB minified JS plus minimal CSS.\n\nInspired by the lightweight workflow ideas in the sdkks/mdviewer fork. Thanks to @sdkks for the implementation input. Attribution belongs in issue/release records, not README or GitHub Pages.

[trsdn]

Shared code-block controls are tracked separately in #26 and must work with the Lite Prism preview renderer.

[trsdn]

Implemented and released in MDViewer+ v2.0.0.