Add a Settings view

[Tosox]

Task Description

As a user, I need a Settings view (accessible from a button in the bottom left of the main window) so that I can configure application behavior without editing config files manually. Settings should apply live where possible without requiring a restart.

Acceptance Criteria

• A "Settings" button is added (to the bottom left of the main UI)
• Clicking it switches the main view to a Settings view with a "Back" button to return
• A General settings group contains:
  • Language selection (calls Localizer.loadLocale() to apply live; a restart may be required if UI components do not
    reflect the change immediately)
  • Download archive handling strategy (keep all / keep latest / delete all)
• An Advanced settings group contains:
  • Log level selection
• All settings are persisted to user_config.yaml
• Settings apply live where possible without requiring a restart

Additional Information

Relevant code: Localizer.loadLocale() for live language switching, MainFrame for UI layout, AppPaths.userConfig for persistence