Flatten panel gradients to subtle purple, themed 404, gold links

- Replace the velvet/ledger diagonal plum gradients with one flat
  purple per surface (anchored to the group-card tone rgb(24,20,29));
  topbar now uses the same flat tone so it meshes with the panels
- Add a Westgate-themed 404 page (Night Masks warning, fa-mask icon),
  vertically centered in the content area; strings in westgate.json
- Set Bootstrap link CSS vars globally so utility-classed links
  (alert-link, link-*) get the wiki gold like plain anchors

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

scss/westgate/_responsive.scss

@@ -1,6 +1,6 @@
 @include media-breakpoint-down(lg) {
 	#panel {
-		background: linear-gradient(180deg, rgba(18, 15, 22, 0.96), rgba(9, 8, 11, 1));
+		background: rgba(17, 14, 21, 0.98);
 	}
 
 	ul.categories-list,