fix: full-width top bar with logo, sidebar below

Restructure layout: top bar spans full width (Pulse logo left, user
actions right) with continuous bottom border. Sidebar sits below with
no vertical border collision. Remove logo from sidebar. Remove all
transition-colors from nav items to prevent white flash on click.

components/dashboard/DashboardShell.tsx

@@ -14,11 +14,13 @@ export default function DashboardShell({
   const { mobileOpen, closeMobile } = useSidebar()
 
   return (
-    <div className="flex h-screen overflow-hidden">
-      <Sidebar siteId={siteId} mobileOpen={mobileOpen} onMobileClose={closeMobile} />
-      <div className="flex-1 flex flex-col min-w-0 overflow-hidden">
-        <UtilityBar />
-        <main className="flex-1 overflow-y-auto">
+    <div className="flex flex-col h-screen overflow-hidden">
+      {/* Top bar: full width — logo left, actions right */}
+      <UtilityBar />
+      {/* Below: sidebar + content */}
+      <div className="flex flex-1 overflow-hidden">
+        <Sidebar siteId={siteId} mobileOpen={mobileOpen} onMobileClose={closeMobile} />
+        <main className="flex-1 min-w-0 overflow-y-auto">
           {children}
         </main>
       </div>