feat(frontend): add relativeTimeDe helper for dashboard meta lines

Pure function with injectable now — lets the dashboard enrichment block
render "vor 2 Min." / "vor 3 Std." / "vor 2 Tagen" without clock-based
test flakiness. Reuses the existing comment_time_minutes / _hours /
_days Paraglide keys, no new translations needed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/lib/relativeTime.ts

@@ -0,0 +1,8 @@
+import * as m from '$lib/paraglide/messages.js';
+
+export function relativeTimeDe(from: Date, now: Date = new Date()): string {
+	const minutes = Math.round((now.getTime() - from.getTime()) / 60_000);
+	if (minutes < 60) return m.comment_time_minutes({ count: minutes });
+	if (minutes < 1440) return m.comment_time_hours({ count: Math.round(minutes / 60) });
+	return m.comment_time_days({ count: Math.round(minutes / 1440) });
+}