Refactor UI layout and introduce safe area constants for improved responsiveness

- Updated App, AppFrame, and AudioTab components to utilize new TOP_SAFE_AREA_PADDING and BOTTOM_SAFE_AREA_PADDING constants for consistent layout adjustments.
- Enhanced Sidebar and MainEditor components for better organization and user experience.
- Improved VoicesTab and ProfileList components by integrating new layout features and removing redundant import functionality.
- Streamlined HistoryTable and ModelManagement components for better visual consistency and interaction.

app/src/lib/constants/ui.ts

@@ -0,0 +1,15 @@
+/**
+ * UI layout constants for safe area padding
+ */
+
+/**
+ * Top safe area padding - height of the drag region bar
+ * Corresponds to Tailwind's pt-12 (3rem / 48px)
+ */
+export const TOP_SAFE_AREA_PADDING = 'pt-12';
+
+/**
+ * Bottom safe area padding - height of the audio player
+ * Corresponds to Tailwind's pb-32 (8rem / 128px)
+ */
+export const BOTTOM_SAFE_AREA_PADDING = 'pb-32';