feat: initialize backend database service architecture and implement frontend schema explorer components

frontend/src/components/Header.tsx

@@ -7,9 +7,19 @@ const Header: React.FC = () => {
   const { darkMode, toggleDarkMode } = useAppStore();
 
   return (
-    <AppBar position="static" color="transparent" elevation={0} sx={{ borderBottom: 1, borderColor: 'divider' }}>
+    <AppBar 
+      position="static" 
+      elevation={0} 
+      sx={{ 
+        borderBottom: 1, 
+        borderColor: 'divider',
+        bgcolor: darkMode ? 'rgba(16, 24, 48, 0.95)' : 'rgba(255, 255, 255, 0.95)',
+        backdropFilter: 'blur(10px)',
+        zIndex: (theme) => theme.zIndex.drawer + 1
+      }}
+    >
       <Toolbar>
-        <Typography variant="h6" sx={{ flexGrow: 1, fontWeight: 700, color: 'primary.main' }}>
+        <Typography variant="h6" sx={{ flexGrow: 1, fontWeight: 800, color: 'primary.main', letterSpacing: -1 }}>
           MARIAVEL
         </Typography>
         <Box sx={{ display: 'flex', alignItems: 'center', gap: 1 }}>