feat: Add back button to insights page

Added back button to UnifiedInsightsDashboard component to match
the navigation pattern used in tracker pages (sleep, feeding, etc).

Changes:
- Added ArrowBack icon import
- Added useRouter hook
- Added IconButton with router.back() onClick handler
- Restructured header to include back button alongside title

Now insights page has consistent navigation with tracker pages.

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

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

maternal-web/components/features/analytics/UnifiedInsightsDashboard.tsx

@@ -13,8 +13,10 @@ import {
   CircularProgress,
   Alert,
   Grid,
+  IconButton,
 } from '@mui/material';
-import { Timeline, TrendingUp, Assessment } from '@mui/icons-material';
+import { Timeline, TrendingUp, Assessment, ArrowBack } from '@mui/icons-material';
+import { useRouter } from 'next/navigation';
 import { childrenApi, Child } from '@/lib/api/children';
 import { analyticsApi, PatternInsights, PredictionInsights } from '@/lib/api/analytics';
 import { InsightsDashboard } from './InsightsDashboard';
@@ -46,6 +48,7 @@ function TabPanel(props: TabPanelProps) {
 }
 
 export function UnifiedInsightsDashboard() {
+  const router = useRouter();
   const { user } = useAuth();
   const [children, setChildren] = useState<Child[]>([]);
   const [selectedChildId, setSelectedChildId] = useState<string>('');
@@ -162,14 +165,19 @@ export function UnifiedInsightsDashboard() {
       transition={{ duration: 0.5 }}
     >
       <Box sx={{ px: { xs: 2, sm: 3 }, py: 3 }}>
-        {/* Header */}
-        <Box sx={{ mb: 3 }}>
-          <Typography variant="h4" gutterBottom fontWeight={600}>
-            Insights & Predictions
-          </Typography>
-          <Typography variant="body2" color="text.secondary">
-            AI-powered insights, patterns, and predictions for your child
-          </Typography>
+        {/* Header with Back Button */}
+        <Box sx={{ display: 'flex', alignItems: 'center', mb: 3 }}>
+          <IconButton onClick={() => router.back()} sx={{ mr: 2 }}>
+            <ArrowBack />
+          </IconButton>
+          <Box>
+            <Typography variant="h4" fontWeight={600}>
+              Insights & Predictions
+            </Typography>
+            <Typography variant="body2" color="text.secondary">
+              AI-powered insights, patterns, and predictions for your child
+            </Typography>
+          </Box>
         </Box>
 
         {/* Error Alert */}