Reorganize admin nav by feature and soften light mode.

Sidebar lists one entry per feature; keep hub tabs only for sibling views (events, tickets, ranks/permissions, moderation, radio, analytics, devops). Soft cool-gray light canvas/surface replaces harsh white.

Co-authored-by: Cursor <[email protected]>

src/app/admin/layout.tsx

@@ -116,6 +116,7 @@ async function Sidebar({
 											key={`${group.labelKey}-${item.href}`}
 											href={item.href}
 											matchPrefixes={item.matchPrefixes}
+											matchExcludePrefixes={item.matchExcludePrefixes}
 											icon={<ItemIcon size={16} />}
 										>
 											{t(item.labelKey)}