- thumbnails: compile the project stylesheet once per rebuild and feed it
into the layout sandbox, compose each tile like the runtime does
(<section data-ps-slide> around the slide), and show example HTML on
the global tile instead of another real slide's content.
- worker: less compiles off the main thread in less-worker; a side-effect
module shims window/document and disables the browser build's page
auto-init, and compilation falls back inline if the worker can't start.
- code-to-element: wrap styles[] entries in <style> blocks - raw CSS text
in the iframe head fell into <body> and rendered as literal garbage.
