Sapper to SvelteKit migration: update package.json (add "type": "module", replace sapper with @sveltejs/kit + adapter), rename config files and templates, rename route files (+page.svelte, +layout.svelte, +error.svelte), update imports (@sapper/app → $app/navigation/$app/stores), rename preload → load with event arg, remove regex routes and segment prop, use root-relative URLs, replace sapper: attributes with data-sveltekit-, remove req/res access.