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/lib/components/PanelMetadata.svelte

@@ -136,9 +136,7 @@ let { doc }: { doc: Doc } = $props();
 							{doc.sender.firstName[0]}{doc.sender.lastName[0]}
 						</div>
 						<div>
-							<p
-								class="font-serif text-ink decoration-brand-mint underline-offset-2 group-hover:underline"
-							>
+							<p class="font-serif text-ink group-hover:underline">
 								{doc.sender.firstName}
 								{doc.sender.lastName}
 							</p>