Enhance user settings for refresh period and network usage

[bossly]

Improve in-app settings to allow users to control wallpaper refresh frequency and network/battery preferences.

Why: Allows users to better customize the behavior to their preferences and device/environment limitations.

Acceptance Criteria:

• Add settings screen/section for refresh frequency (user-selectable period).
• Option to run only on WiFi or with battery-saver mode disabled.
• Preferences persist across device restarts, reflected in scheduler logic.
• Add relevant UI elements and descriptions so users know what is being configured.

Next steps:

• Modify settings/preferences and related UI code.
• Integrate new options into scheduler/background task logic.