fix(layout): replace hardcoded 'Hochladen' with m.upload_action() + aria-label

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

frontend/src/routes/+layout.svelte

@@ -2,6 +2,7 @@
 import './layout.css';
 import { page } from '$app/state';
 import { onMount } from 'svelte';
+import * as m from '$lib/paraglide/messages.js';
 import LanguageSwitcher from '$lib/components/LanguageSwitcher.svelte';
 import ThemeToggle from '$lib/components/ThemeToggle.svelte';
 import NotificationBell from '$lib/components/NotificationBell.svelte';
@@ -55,6 +56,7 @@ const userInitials = $derived.by(() => {
 						{#if data?.user}
 							<a
 								href="/documents/new"
+								aria-label={m.upload_action()}
 								class="inline-flex items-center gap-2 rounded-sm border border-white/25 px-3.5 py-1.5 font-sans text-[11px] font-bold tracking-[.12em] text-white uppercase transition-colors hover:bg-white/10"
 							>
 								<svg
@@ -73,7 +75,7 @@ const userInitials = $derived.by(() => {
 									<polyline points="17 8 12 3 7 8" />
 									<line x1="12" y1="3" x2="12" y2="15" />
 								</svg>
-								Hochladen
+								{m.upload_action()}
 							</a>
 						{/if}
 						<!-- Language selector (desktop only — mobile lives in nav drawer) -->