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/_tokens.scss

@@ -105,12 +105,7 @@
 	--wg-border-soft: rgba(194, 163, 90, 0.08);
 	--wg-focus: rgba(194, 163, 90, 0.28);
 	--wg-focus-ring: #c2a35a;
-	--wg-ledger-panel: linear-gradient(
-		100deg,
-		rgba(38, 22, 35, 0.5) 0%,
-		rgba(19, 17, 24, 0.97) 34%,
-		rgba(13, 12, 17, 0.98) 100%
-	);
+	--wg-ledger-panel: rgba(21, 17, 26, 0.97);
 	--wg-ledger-ruling: rgba(194, 163, 90, 0.055);
 	--wg-ledger-rule-strong: rgba(194, 163, 90, 0.16);
 	--wg-ledger-border: rgba(194, 163, 90, 0.18);
@@ -120,20 +115,8 @@
 		--wg-ledger-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.024), inset 0 -1px 0 rgba(0, 0, 0, 0.42), 0 8px 18px rgba(0, 0, 0, 0.2);
 		--wg-etched-highlight: rgba(246, 223, 163, 0.34);
 		--wg-etched-shadow: rgba(23, 12, 16, 0.82);
-		--wg-velvet-panel: linear-gradient(
-		100deg,
-		rgba(42, 18, 34, 0.46) 0%,
-		rgba(25, 22, 31, 0.95) 23%,
-		rgba(18, 16, 23, 0.99) 62%,
-		rgba(13, 12, 17, 0.98) 100%
-	);
-	--wg-velvet-panel-hover: linear-gradient(
-		100deg,
-		rgba(58, 24, 48, 0.56) 0%,
-		rgba(31, 25, 39, 0.98) 23%,
-		rgba(21, 18, 27, 1) 62%,
-		rgba(15, 14, 20, 0.99) 100%
-	);
+	--wg-velvet-panel: rgba(24, 20, 29, 0.97);
+	--wg-velvet-panel-hover: rgba(31, 26, 38, 0.98);
 	--wg-velvet-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.025), inset 0 0 34px rgba(96, 32, 68, 0.11), 0 10px 26px rgba(0, 0, 0, 0.24);
 	--wg-control-bg: linear-gradient(to bottom, rgba(194, 163, 90, 0.15), rgba(194, 163, 90, 0.05));
 }