dmenu ipc for spotlight

## Feature Description
It would be very nice to have a dmenu mode with an ipc command like how standalone launchers like rofi/wofi/fuzzel do.

## Use Case
This really helps when you have a lot of scripts and want to bind it in a wm shortcut and you want to be able to choose an option for it or even used to get a text user input without options.

## Compositor

Is this feature specific to one compositor?

- [x] All compositors
- [ ] niri
- [ ] Hyprland
- [ ] dwl (MangoWC)
- [ ] sway

## Proposed Solution

example command:
```sh
printf '%s\n' 'option1' 'option2' 'option3' | dms ipc dmenu
```
It can have these options:
- choose a different separator than '\n'
- only-prompt mode (get input without options)
- change the default input placeholder

## Alternatives/Existing Solutions
using other standalone launchers with dmenu mode or using dmenu itself

Start by tracing the existing `dms ipc` command entry point and how standalone launcher modes are handled. Compare the proposed `printf ... | dms ipc dmenu` flow with the existing IPC behavior, then define completion around selecting an input option or accepting prompt-only text, with configurable separators and placeholders.

Written by the indexing model from the issue text.