refactor: successfully refactored the SettingsPage UI

The changes include:

1. Adding descriptive paragraphs at the top of the main settings page and within the "Appearance" section, using the newly defined localization keys.
2. Refactoring the "Appearance" tab to use `ExpansionTile`s for "Theme Settings" and "Font Settings" instead of nested `TabBar`s, which improves visual clarity and user experience.

Author: fulleni