feat: Enhance dark mode support and improve UI components

Commit notes

This commit introduces custom dark mode styles in app.css, ensuring smooth transitions between light and dark themes. It also updates various components, including BarControls, BpmControl, and GainMeter, to enhance user interaction and visual feedback. New GrooveControls and KeyboardShortcuts components are added to improve functionality and user experience. Additionally, the sequencer store is updated to manage groove settings, and the layout is modified to apply dark mode based on system preferences.