Fix Expo Router conflicting routes and update dependencies (#32)

- Remove duplicate route file app/sessions/[id].tsx that conflicted with app/sessions/[id]/index.tsx
- Update Expo SDK packages to resolve version mismatches with SDK 54
- Update dev dependencies (@types/jest, @types/react, jest-expo) to SDK 54-compatible versions
- Install expo-linear-gradient dependency required by react-native-gifted-charts
- Resolve all npm security vulnerabilities

Fixes routing error: "Found conflicting screens with the same pattern"

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Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: jeremyeder