style(layout): sidebar stripe + topbar gradient + bell spring + search ring

Sidebar active items: 4px brand left-edge stripe (rounded-r-full) replacing the
border-l-2 + bg shift; section header smaller-caps + brand-200 colour; user-footer
avatar gets shadow-sm + ring-2 ring-white/30.

Topbar '+ New' uses bg-gradient-brand with shadow-sm + scale-1.02 hover. User
avatar trigger gets shadow-sm + ring-2 ring-white. Notification badge gets
gradient-brand fill + ring-2 ring-background + animate-badge-pop spring keyframe
(retriggers on count change via key={unreadCount}). Command search gets shadow-xs
inset + brand focus ring (ring-4 ring-brand/15).

Adds badge-pop keyframes to tailwind config.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/notifications/notification-bell.tsx

@@ -57,7 +57,10 @@ export function NotificationBell() {
         <Button variant="ghost" size="icon" className="relative">
           <Bell className="h-5 w-5" />
           {unreadCount > 0 && (
-            <span className="absolute -top-0.5 -right-0.5 flex h-4 w-4 items-center justify-center rounded-full bg-blue-500 text-[10px] font-bold text-white">
+            <span
+              key={unreadCount}
+              className="absolute -top-0.5 -right-0.5 flex h-4 w-4 items-center justify-center rounded-full bg-gradient-brand text-[10px] font-bold text-white shadow-sm ring-2 ring-background animate-badge-pop"
+            >
               {unreadCount > 99 ? '99+' : unreadCount}
             </span>
           )}