feat: Implement application preferences with JSON persistence

- Added preferences management in `preferences.py` with functions to load, save, get, set, and reset preferences.
- Introduced a configuration directory structure based on the operating system.
- Integrated preferences into the settings window, allowing users to reset settings and manage window geometry.
- Enhanced `search_filter.py` to support flexible date column names and improved filtering logic.
- Updated `settings_window.py` to include options for managing backup and configuration folder paths.
- Introduced an `UndoManager` class to handle undo actions for add/update/delete operations.
- Improved UIManager to support sorting in tree views and added a toast notification feature.

USER_GUIDE.md

@@ -398,6 +398,28 @@ TheChart application supports comprehensive keyboard shortcuts for improved prod
 - **Double-click**: Edit entry - Opens the edit dialog for the selected entry
 
 ### Help
+### Backup and Restore
+
+#### Creating Backups
+- Automatic backups are created on startup and shutdown
+- Manual backups: Tools → Create Backup Now (Ctrl+Shift+B)
+- Backups are stored in your backups folder (Tools → Open Backups Folder)
+
+#### Restoring from Backup
+You can restore the main CSV from a previous backup file.
+
+Steps:
+1. Open Tools → Restore from Backup… (or press Ctrl+Shift+R)
+2. Select a backup CSV file from the backups folder
+3. Review the confirmation dialog (file name, size, last modified)
+4. Confirm to proceed
+
+Notes:
+- A safety backup of the current data is created automatically before restore
+- After restore, the table and graph refresh automatically
+- The status bar shows the result and a brief toast confirms success
+- Use Tools → Open Backups Folder to locate backup files quickly
+
 - **F1**: Show keyboard shortcuts help - Displays a dialog with all available keyboard shortcuts
 
 ### Implementation Details