feat: implement base landing page and initial React frontend layout with sidebar navigation

frontend/src/App.tsx

@@ -2,9 +2,9 @@ import React, { useMemo, useEffect } from 'react';
 import { ThemeProvider, CssBaseline, Box } from '@mui/material';
 import { getTheme } from './theme/theme';
 import { useAppStore } from './store/useAppStore';
-import Sidebar from './components/Sidebar';
-import MainContent from './components/MainContent';
-import Header from './components/Header';
+import Sidebar from './components/Sidebar.tsx';
+import MainContent from './components/MainContent.tsx';
+import Header from './components/Header.tsx';
 
 const App: React.FC = () => {
   const darkMode = useAppStore((state) => state.darkMode);

frontend/src/components/Sidebar.tsx

@@ -26,7 +26,16 @@ const Sidebar: React.FC = () => {
               <ListItemIcon>
                 <Storage color={activeDatabase === db ? 'primary' : 'inherit'} />
               </ListItemIcon>
-              <ListItemText primary={db} primaryTypographyProps={{ variant: 'body2', fontWeight: activeDatabase === db ? 600 : 400 }} />
+              <ListItemText 
+                primary={
+                  <Typography 
+                    variant="body2" 
+                    sx={{ fontWeight: activeDatabase === db ? 600 : 400 }}
+                  >
+                    {db}
+                  </Typography>
+                } 
+              />
             </ListItemButton>
           </ListItem>
         ))}