feat: replace sidebar with 21st.dev hover-to-expand component

Use framer-motion animated sidebar from 21st.dev — collapses to icons,
expands on hover. Phosphor icons instead of lucide. Remove old manual
collapse/expand and sidebar-context. Top bar has Pulse logo + user
actions, sidebar below with site picker and nav groups.

components/dashboard/DashboardShell.tsx

@@ -1,8 +1,7 @@
 'use client'
 
-import Sidebar from './Sidebar'
+import PulseSidebar from './Sidebar'
 import UtilityBar from './UtilityBar'
-import { useSidebar } from '@/lib/sidebar-context'
 
 export default function DashboardShell({
   siteId,
@@ -11,15 +10,11 @@ export default function DashboardShell({
   siteId: string
   children: React.ReactNode
 }) {
-  const { mobileOpen, closeMobile } = useSidebar()
-
   return (
     <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} />
+        <PulseSidebar siteId={siteId} />
         <main className="flex-1 min-w-0 overflow-y-auto">
           {children}
         </main>