css: consolidate stylesheets into single source of truth

Merge nordtheme.css tokens and utility classes into app.css, import
app.css once in root layout, delete redundant files (nordtheme.css,
form.css, rosenkranz.css), move domain CSS to layouts, fix broken
shake keyframe in action_button.css, and scope form styles to the
two pages that need them. 10 CSS files → 6, 41 redundant imports removed.

src/routes/[recipeLang=recipeLang]/add/+page.svelte

@@ -10,7 +10,6 @@
 	import CreateStepList from '$lib/components/recipes/CreateStepList.svelte';
 	import Toggle from '$lib/components/Toggle.svelte';
 	import '$lib/css/action_button.css';
-	import '$lib/css/nordtheme.css';
 
 	let { data, form }: { data: PageData; form: ActionData } = $props();