feat: add svelte 5 + cornerstone project

[mcullifer]

• Adds new svelte 5 project with example cornerstone viewport

The example project uses SvelteKit which by default has SSR enabled. It shows how to use $effect runes to initialize cornerstone and render the viewport once it's client side. You can add any number of viewports inside the <CornerstoneContext>...</CornerstoneContext> block which will scope an engine instance to the children() #snippet. If multiple contexts exist with the same engineId then it will re-use the existing one. The onReady events for <CornerstoneContext /> and <CornerstoneViewport /> have an optional cleanup function return value. The example shows how you can use this to clean up resources after a page navigation or some state change that unmounts them from the DOM.

To run: npm install & npm run dev