fix(bulk-upload): i18n topbar title; replace hardcoded German strings

'Neues Dokument' / 'Neue Dokumente' in BulkDocumentEditLayout topbar
bypassed Paraglide. Added bulk_title_single and bulk_title_multi keys
to de/en/es message files and switched to m.*() calls.

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

frontend/src/lib/components/document/BulkDocumentEditLayout.svelte

@@ -146,7 +146,7 @@ async function save() {
 		</a>
 		<span class="text-ink-3" aria-hidden="true">·</span>
 		<span class="font-serif text-sm font-bold text-ink">
-			{isMulti ? 'Neue Dokumente' : 'Neues Dokument'}
+			{isMulti ? m.bulk_title_multi() : m.bulk_title_single()}
 		</span>
 		{#if isMulti}
 			<span class="ml-auto flex items-center gap-3">