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/_widgets.scss

@@ -54,7 +54,7 @@
 	padding: var(--wg-space-md);
 	background:
 		linear-gradient(to bottom, transparent calc(100% - 1px), rgba(194, 163, 90, 0.045) calc(100% - 1px)),
-		linear-gradient(100deg, rgba(42, 18, 34, 0.34), rgba(18, 16, 23, 0.96) 62%, rgba(13, 12, 17, 0.98)) !important;
+		var(--wg-velvet-panel) !important;
 	background-size: 100% var(--wg-ledger-line), auto;
 	border: 1px solid rgba(194, 163, 90, 0.14);
 	border-radius: 8px;