Retheme UI from blue to neutral zinc backgrounds with indigo accents

Removes the blue tint from all dark-mode surfaces by switching CSS
variables to zinc-based neutrals, and replaces decorative blue classes
with indigo across buttons, focus rings, tabs, and links. Semantic blue
(severity badges, status badges, role badges, timeline markers) is
preserved.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

client/src/pages/MyTickets.tsx

@@ -39,7 +39,7 @@ export default function MyTickets() {
             <Link
               key={ticket.id}
               to={`/${ticket.displayId}`}
-              className="flex items-center gap-4 bg-gray-900 border border-gray-800 rounded-lg px-4 py-3 hover:border-blue-500/50 transition-all group"
+              className="flex items-center gap-4 bg-gray-900 border border-gray-800 rounded-lg px-4 py-3 hover:border-indigo-500/50 transition-all group"
             >
               <div
                 className={`w-1 self-stretch rounded-full flex-shrink-0 ${
@@ -66,7 +66,7 @@ export default function MyTickets() {
                     {ticket.category.name} › {ticket.type.name} › {ticket.item.name}
                   </span>
                 </div>
-                <p className="text-sm font-medium text-gray-200 truncate group-hover:text-blue-400">
+                <p className="text-sm font-medium text-gray-200 truncate group-hover:text-indigo-400">
                   {ticket.title}
                 </p>
               </div>