feat: Dokploy-style sidebar layout for site pages

Sidebar takes full viewport height with Pulse logo at top. No Header
on site pages — UtilityBar in content area provides theme toggle, app
launcher, notifications, and user menu. Non-site authenticated pages
keep static Header. No footer on dashboard pages.

components/dashboard/DashboardShell.tsx

@@ -1,6 +1,7 @@
 'use client'
 
 import Sidebar from './Sidebar'
+import UtilityBar from './UtilityBar'
 import { useSidebar } from '@/lib/sidebar-context'
 
 export default function DashboardShell({
@@ -13,11 +14,14 @@ export default function DashboardShell({
   const { mobileOpen, closeMobile } = useSidebar()
 
   return (
-    <div className="flex flex-1 overflow-hidden">
+    <div className="flex h-screen overflow-hidden">
       <Sidebar siteId={siteId} mobileOpen={mobileOpen} onMobileClose={closeMobile} />
-      <main className="flex-1 min-w-0 overflow-y-auto">
-        {children}
-      </main>
+      <div className="flex-1 flex flex-col min-w-0 overflow-hidden">
+        <UtilityBar />
+        <main className="flex-1 overflow-y-auto">
+          {children}
+        </main>
+      </div>
     </div>
   )
 }