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/search/command-search.tsx

@@ -84,8 +84,10 @@ export function CommandSearch() {
       {/* ── Single persistent search bar ── */}
       <div
         className={cn(
-          'flex items-center gap-2 rounded-md border bg-background px-2.5 transition-all duration-150',
-          focused ? 'border-muted-foreground/40 w-64 lg:w-80' : 'w-44 lg:w-60',
+          'flex items-center gap-2 rounded-md border bg-background px-2.5 shadow-xs transition-all duration-base ease-smooth',
+          focused
+            ? 'border-brand/60 ring-4 ring-brand/15 w-64 lg:w-80'
+            : 'border-input w-44 lg:w-60',
         )}
       >
         <Search className="h-4 w-4 shrink-0 text-muted-foreground" />