style: standardise link hover underline (2px, offset-4, accent) globally

Move text-decoration-thickness/underline-offset into the global a:hover
base rule so every link that shows an underline on hover gets identical
treatment: 2px thick, 4px offset, accent colour.

Remove the now-redundant per-component decoration-brand-mint / decoration-
accent / decoration-2 / underline-offset-{2,4} utilities from DocumentList,
enrich, persons, PersonDocumentList, and PanelMetadata.

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

frontend/src/routes/enrich/+page.svelte

@@ -74,9 +74,7 @@ const count = $derived(documents.length);
 					<li class="group transition-colors duration-200 hover:bg-muted">
 						<a href="/enrich/{doc.id}" class="flex items-center justify-between p-6">
 							<div class="min-w-0 flex-1">
-								<p
-									class="font-serif text-lg font-medium text-ink decoration-accent decoration-2 underline-offset-4 group-hover:underline"
-								>
+								<p class="font-serif text-lg font-medium text-ink group-hover:underline">
 									{doc.title}
 								</p>
 							</div>