Implement Phase 7 Performance Optimization and fix tracking system

Phase 7 Implementation:
- Add lazy loading for AI Assistant and Insights pages
- Create LoadingFallback component with skeleton screens (page, card, list, chart, chat variants)
- Create OptimizedImage component with Next.js Image optimization
- Create PerformanceMonitor component with web-vitals v5 integration
- Add performance monitoring library tracking Core Web Vitals (CLS, INP, FCP, LCP, TTFB)
- Install web-vitals v5.1.0 dependency
- Extract AI chat interface and insights dashboard to lazy-loaded components

Tracking System Fixes:
- Fix API data transformation between frontend (timestamp/data) and backend (startedAt/metadata)
- Update createActivity, getActivities, and getActivity to properly transform data structures
- Fix diaper, feeding, and sleep tracking pages to work with backend API

Homepage Improvements:
- Connect Today's Summary to backend daily summary API
- Load real-time data for feeding count, sleep hours, and diaper count
- Add loading states and empty states for better UX
- Format sleep duration as "Xh Ym" for better readability
- Display child name in summary section

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

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

maternal-web/app/track/sleep/page.tsx

@@ -34,6 +34,8 @@ import {
   DirectionsCar,
   Chair,
   Home,
+  ChildCare,
+  Add,
 } from '@mui/icons-material';
 import { useRouter } from 'next/navigation';
 import { AppShell } from '@/components/layouts/AppShell/AppShell';
@@ -330,18 +332,24 @@ export default function SleepTrackPage() {
     return (
       <ProtectedRoute>
         <AppShell>
-          <Box>
-            <Alert severity="warning">
-              Please add a child first before tracking sleep activities.
-            </Alert>
-            <Button
-              variant="contained"
-              onClick={() => router.push('/children')}
-              sx={{ mt: 2 }}
-            >
-              Go to Children Page
-            </Button>
-          </Box>
+          <Card>
+            <CardContent sx={{ textAlign: 'center', py: 8 }}>
+              <ChildCare sx={{ fontSize: 64, color: 'text.secondary', mb: 2 }} />
+              <Typography variant="h6" color="text.secondary" gutterBottom>
+                No Children Added
+              </Typography>
+              <Typography variant="body2" color="text.secondary" sx={{ mb: 3 }}>
+                You need to add a child before you can track sleep activities
+              </Typography>
+              <Button
+                variant="contained"
+                startIcon={<Add />}
+                onClick={() => router.push('/children')}
+              >
+                Add Child
+              </Button>
+            </CardContent>
+          </Card>
         </AppShell>
       </ProtectedRoute>
     );