Add icon mapping to Notifications widget

### Feature Description

This works great with the **Workspace Switcher** widget, so I'd like to see it added to the **Notifications** widget.

### Use Case

Just more visually pleasing, nothing more.

### Compositor(s)

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

### Proposed Solution

_No response_

### Alternatives/Existing Solutions

_No response_

Start by locating the Notifications widget and the existing icon mapping in the Workspace Switcher widget. Compare how the two widgets obtain and display application information under Hyprland. Done means the Notifications widget shows the intended application icons without affecting other compositor configurations.

Written by the indexing model from the issue text.