Peakk2011/cygnus ? reverse-engineered prompt

Build me a lightweight HTML preprocessor for native .html files that works as a Vite plugin. I want to be able to write normal HTML, then add simple directives for things like setting the page title and head content, reusing components from other HTML files, injecting CSS, and defining small reusable variables. It should also support a tiny runtime helper for toggling classes from buttons or other elements.

Please make it feel like a library, not a framework, so I can install it, import one plugin into vite.config.js, and use it in an existing project without any special scaffolding. Include a simple starter setup with a sample vite.config.js, an index.html, and a README that explains the syntax in plain English. If you need to check anything, look up the current Vite docs online first.