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/_controls.scss

@@ -397,7 +397,7 @@ table[component="notification/table"] a[data-type]:focus {
       transparent calc(100% - 1px),
       rgba(194, 163, 90, 0.055) calc(100% - 1px)
     ),
-    linear-gradient(100deg, rgba(32, 19, 30, 0.98), rgba(13, 12, 17, 0.98)) !important;
+    var(--wg-velvet-panel) !important;
   background-size:
     100% var(--wg-ledger-line),
     auto;