Add Phase 2 & 3: Web frontend with authentication and tracking features

- Initialize Next.js 14 web application with Material UI and TypeScript
- Implement authentication (login/register) with device fingerprint
- Create mobile-first responsive layout with app shell pattern
- Add tracking pages for feeding, sleep, and diaper changes
- Implement activity history with filtering
- Configure backend CORS for web frontend (port 3030)
- Update backend port to 3020, frontend to 3030
- Fix API response handling for auth endpoints

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

maternal-web/components/layouts/TabBar/TabBar.tsx

@@ -0,0 +1,63 @@
+'use client';
+
+import { usePathname, useRouter } from 'next/navigation';
+import { BottomNavigation, BottomNavigationAction, Paper } from '@mui/material';
+import {
+  Home,
+  Timeline,
+  Chat,
+  Insights,
+  Settings,
+} from '@mui/icons-material';
+
+export const TabBar = () => {
+  const router = useRouter();
+  const pathname = usePathname();
+
+  const tabs = [
+    { label: 'Home', icon: <Home />, value: '/' },
+    { label: 'Track', icon: <Timeline />, value: '/track' },
+    { label: 'AI Chat', icon: <Chat />, value: '/ai-assistant' },
+    { label: 'Insights', icon: <Insights />, value: '/insights' },
+    { label: 'Settings', icon: <Settings />, value: '/settings' },
+  ];
+
+  return (
+    <Paper
+      sx={{
+        position: 'fixed',
+        bottom: 0,
+        left: 0,
+        right: 0,
+        zIndex: 1000,
+      }}
+      elevation={3}
+    >
+      <BottomNavigation
+        value={pathname}
+        onChange={(event, newValue) => {
+          router.push(newValue);
+        }}
+        showLabels
+        sx={{
+          height: 64,
+          '& .MuiBottomNavigationAction-root': {
+            minWidth: 60,
+            '&.Mui-selected': {
+              color: 'primary.main',
+            },
+          },
+        }}
+      >
+        {tabs.map((tab) => (
+          <BottomNavigationAction
+            key={tab.value}
+            label={tab.label}
+            icon={tab.icon}
+            value={tab.value}
+          />
+        ))}
+      </BottomNavigation>
+    </Paper>
+  );
+};