Refactor: Enhance API structure and improve frontend navigation

Commit notes

This commit includes several key updates:

- **Backend Changes**: - Added a new function `precreateSampleR2Key` to ensure the `r2_key` column is created as nullable before migration, preventing potential migration failures. - Updated the `Migrate` function to include pre-migration checks for the `samples` table.

- **Frontend Changes**: - Refactored route structure to improve navigation, including the addition of new routes for the app's library and studio sections. - Updated the `Header` component to reflect new navigation paths and improved layout. - Enhanced the `StorageDashboard` and `EnhancedSampleLibrary` components for better user experience and consistency in UI elements.

These changes aim to streamline the application structure and enhance user navigation across the platform.