Add theme management and settings functionality

- Introduced `ThemeManager` to handle application themes using `ttkthemes`.
- Added `SettingsWindow` for user preferences including theme selection and UI settings.
- Integrated theme selection into the main application with a menu for quick access.
- Enhanced UI components with custom styles based on the selected theme.
- Implemented tooltips for better user guidance across various UI elements.
- Updated dependencies to include `ttkthemes` for improved visual appeal.

pyproject.toml

@@ -12,6 +12,7 @@ dependencies = [
     "pandas>=2.3.1",
     "reportlab>=4.4.3",
     "tk>=0.1.0",
+    "ttkthemes>=3.2.2",
 ]
 
 [dependency-groups]