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/DocumentList.svelte

@@ -56,9 +56,7 @@ let {
 							<!-- Main Info -->
 							<div class="flex-1">
 								<div class="mb-2 flex items-baseline justify-between">
-									<h3
-										class="font-serif text-xl font-medium text-ink decoration-brand-mint decoration-2 underline-offset-4 group-hover:underline"
-									>
+									<h3 class="font-serif text-xl font-medium text-ink group-hover:underline">
 										{doc.title || doc.originalFilename}
 									</h3>
 								</div>