expose DMS menu entries as .desktop files

### Feature Description

Currently, DMS entries in the launcher like settings and system monitor only show up in spotlight or other DMS launchers. I think these should create .desktop files.

### Use Case

If you're using a different launcher, such as Vicinae, you don't have a way to launch these by default. It would be great to include .desktop files for these in the project so that they'll work out of the box with other launchers.

### Compositor(s)

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

### Proposed Solution

Right now, the entries are [hardcoded](https://github.com/AvengeMedia/DankMaterialShell/blob/1f2e231386ab5a2bf622c52c31833f3506a09704/quickshell/Services/AppSearchService.qml#L151C2-L195) into the launcher. If .desktop files were created, they could be removed.

The launcher tab of the settings lets you toggle if these are shown, which could be done by instead having it create and remove the files, or it could just append `Hidden=true` to the files.

### Alternatives/Existing Solutions

You can already work around this by creating desktop files with the correct IPC calls, but it seems unnecessary to have to that.

Start in quickshell/Services/AppSearchService.qml at the hardcoded launcher entries, then inspect the launcher tab of settings and how its visibility toggle is handled. Done means the DMS entries are available as .desktop files for other launchers and the existing hardcoded entries and visibility behavior are replaced or correctly integrated.

Written by the indexing model from the issue text.