Make light/dark mode toggles consistent

### Feature Description

Currently, the toggles for light/dark mode are not consistent. In the Control Center, you toggle it on for dark mode, but in Settings > Theme & Colours, you toggle it on for light mode. They should be the same.

### Use Case

It would make DMS more consistent.

### Compositor(s)

- [x] All compositors
- [ ] Niri
- [ ] Hyprland
- [ ] MangoWC (dwl)
- [ ] Sway
- [ ] Other (specify below)

### Proposed Solution

_No response_

### Alternatives/Existing Solutions

_No response_

Start at the light/dark mode toggle in the Control Center and the toggle in Settings > Theme & Colours, comparing which state each control represents. Done means both toggles use the same meaning for their on and off states across all compositors.

Written by the indexing model from the issue text.