fix: load Sidebar with ssr:false — zero server-rendered content

The sidebar now uses next/dynamic with ssr:false, meaning it renders
NOTHING in the server HTML. No DOM content = no possible flash of
"Ci" or any text during SSR-to-hydration gap. The sidebar only mounts
on the client where localStorage is immediately available, so
collapsed state is correct from the very first render.

components/dashboard/DashboardShell.tsx

@@ -1,9 +1,12 @@
 'use client'
 
 import { useState, useCallback } from 'react'
-import Sidebar from './Sidebar'
+import dynamic from 'next/dynamic'
 import ContentHeader from './ContentHeader'
 
+// Load sidebar only on the client — prevents any SSR flash of text/labels
+const Sidebar = dynamic(() => import('./Sidebar'), { ssr: false })
+
 export default function DashboardShell({
   siteId,
   children,