refactor: move shared components to lib/shared/ sub-packages

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/shared/primitives/LanguageSwitcher.svelte

@@ -0,0 +1,26 @@
+<script lang="ts">
+import { setLocale, getLocale } from '$lib/paraglide/runtime';
+
+let { inverted = false }: { inverted?: boolean } = $props();
+
+const locales = ['DE', 'EN', 'ES'] as const;
+const localeMap = { DE: 'de', EN: 'en', ES: 'es' } as const;
+const activeLocale = $derived(getLocale().toUpperCase());
+</script>
+
+{#each locales as locale (locale)}
+	<button
+		type="button"
+		onclick={() => setLocale(localeMap[locale])}
+		class="rounded px-1 font-sans tracking-widest transition-colors focus:outline-none focus-visible:ring-2 focus-visible:ring-focus-ring
+               {activeLocale === locale
+			? inverted
+				? 'font-bold text-white'
+				: 'font-bold text-ink'
+			: inverted
+				? 'font-normal text-white/70 hover:text-white'
+				: 'font-normal text-ink-3 hover:text-ink'}"
+	>
+		{locale}
+	</button>
+{/each}