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