Demo popup: show on every dashboard visit, add upload notice (v2.2.4)

- Popup now shows every time user visits dashboard (not session-cached)
- Only shows on dashboard, not other pages
- Added upload disabled notice with amber highlight
- Upload listed as first full-version feature

client/src/App.jsx

@@ -87,7 +87,6 @@ export default function App() {
   return (
     <TranslationProvider>
       <ToastContainer />
-      {demoMode && isAuthenticated && <DemoBanner />}
       <Routes>
         <Route path="/" element={<RootRedirect />} />
         <Route path="/login" element={<LoginPage />} />