fix(documents): always render undated badge in DocumentRow desktop column

The desktop right-column kept a leftover {#if doc.documentDate}…{:else}—{/if}
fallback that emitted a bare em-dash for undated documents, while the mobile
block already always rendered <DocumentDate>. DocumentDate defensively maps a
null date to the "Datum unbekannt" badge, so render it unconditionally — an
undated document is an absence, not an error, and never shows a bare "—".

Refs #668

frontend/src/lib/document/DocumentRow.svelte

@@ -187,16 +187,15 @@ function safeTagColor(color: string | null | undefined): string {
 			<!-- Right column — desktop only -->
 			<div class="hidden flex-col gap-2 pl-4 font-sans text-sm text-ink-2 sm:flex sm:w-44 lg:w-56">
 				<div>
-					{#if doc.documentDate}
+					<!-- An undated document is an absence, not an error (#668): DocumentDate
+					     defensively maps a null date to the "Datum unbekannt" badge, so we
+					     always render it — never a bare em-dash fallback. -->
 					<DocumentDate
 						iso={doc.documentDate}
 						precision={doc.metaDatePrecision}
 						end={doc.metaDateEnd}
 						showRaw={false}
 					/>
-					{:else}
-						—
-					{/if}
 				</div>
 				<div>
 					<span class="font-bold tracking-wide text-ink-3 uppercase">{m.docs_list_from()}</span>