feat(#145): internationalise dashboard widget strings (de/en/es)

Replace all hardcoded German strings in dashboard components with
Paraglide translation keys. Date locale uses getLocale() instead
of the hardcoded 'de-DE'.

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

frontend/src/lib/components/DashboardResumeStrip.svelte

@@ -1,5 +1,6 @@
 <script lang="ts">
 import { onMount } from 'svelte';
+import * as m from '$lib/paraglide/messages.js';
 
 interface LastVisited {
 	id: string;
@@ -28,9 +29,9 @@ onMount(() => {
 		data-testid="resume-strip"
 		class="flex items-center gap-2 rounded-sm border border-line bg-surface px-4 py-3 font-sans text-sm"
 	>
-		<span class="text-ink-2">Zuletzt geöffnet:</span>
+		<span class="text-ink-2">{m.dashboard_resume_label()}</span>
 		<a href="/documents/{lastVisited.id}" class="font-medium text-ink hover:underline">
-			{lastVisited.title || 'Zuletzt geöffnet'}
+			{lastVisited.title || m.dashboard_resume_fallback()}
 		</a>
 	</div>
 {/if}