Integrates Objectbox database initialization into the main application startup process.
Adds `path` and `path_provider` as direct dependencies, which are typically required for Objectbox to locate the database directory.
Replaces hardcoded colors and standard Theme.of(context) accesses with a custom AppTheme.
Introduces distinct light and dark themes and persists the selected theme mode using shared_preferences.
Integrates the theme into the main app structure and applies it to various components and pages.
Adds google_fonts dependency for theme typography.