Ipc command to act on the last notification

### Feature Description

It would be equivalent to pressing "enter" on the notification list.

### Use Case

_No response_

### Compositor(s)

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

### Proposed Solution

_No response_

### Alternatives/Existing Solutions

_No response_

Start by locating the IPC command handling and the notification-list action that pressing Enter invokes. Trace how the last notification is selected, then verify that the new command produces the same action across the supported compositor integrations.

Written by the indexing model from the issue text.