[Feature Request] Follow system theme in “Force Dark Mode”

Please add an option for **Force Dark Mode** to **follow the Android system theme** (light/dark) automatically.

Currently, force-dark can be scheduled by time; an additional “Follow system” mode would improve consistency and reduce manual toggling.

### Motivation / Use case

* Many users keep Android set to **“Dark theme”** globally or let the **system auto-switch** (e.g., based on sunset/sunrise).
* When NativeAlpha’s force-dark is tied only to a time schedule, it can **fall out of sync** with the system theme (traveling across time zones, daylight saving changes, or users who switch theme manually).
* Following the system ensures **uniform appearance** across apps and websites, without extra maintenance.

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Thank you for the great app and for considering this enhancement!