Flat purple panels, themed 404, global gold links (#23)

- Replaces the diagonal plum/velvet panel gradients with flat subtle purples (anchored to the group-card tone `rgb(24,20,29)`); the topbar uses the same flat tone so it meshes with the panels.
- Adds a Westgate-themed 404 page ("You've wandered off the map." / Night Masks warning) with a mask icon, vertically centered in the content area. Strings live in `languages/en-GB/westgate.json`.
- Sets Bootstrap link CSS variables globally so utility-classed links (`alert-link`, `link-*`) get the wiki gold like plain anchors already did. Topic-title parchment override is untouched.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Reviewed-on: #23
Co-authored-by: vickydotbat <vickydotbat@tutamail.com>
Co-committed-by: vickydotbat <vickydotbat@tutamail.com>

scss/westgate/_surfaces.scss

@@ -5,6 +5,10 @@ body {
 }
 
 body {
+  --bs-link-color: var(--wg-gold);
+  --bs-link-color-rgb: 194, 163, 90;
+  --bs-link-hover-color: #e0c878;
+  --bs-link-hover-color-rgb: 224, 200, 120;
   font-family: var(--wg-font-text);
   -webkit-font-smoothing: antialiased;
   -moz-osx-font-smoothing: grayscale;
@@ -14,6 +18,12 @@ body {
   background: var(--wg-bg);
 }
 
+// h-100 on #content collapses inside the flex-grown #panel, so the 404's
+// flex-fill never gets height to center in; let #content grow instead
+body.template-404 #content {
+  flex-grow: 1;
+}
+
 .layout-container,
 #content {
   color: var(--wg-text-soft);