Power Menu Improvements

## Feature Description

When There Is Update Installed & Requires Restart It Should Have Update & Shutdown, Update & Restart.
Also When Applications Trigger Power Menu (Like Discover Shows After Update), It Should Trigger DMS Power Menu Instead Of Distro's Power Menu (As It Doesn't Work When Using Niri As Session).

## Use Case

Better UI/UX & Functionality Improvement.

## Compositor

Is this feature specific to one compositor?

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

## Proposed Solution

Improved Power Menu

Start by locating the DMS power-menu entry point and the paths used when Discover or another application invokes the system menu. Trace update-required shutdown and restart behavior across the listed compositors; done means DMS handles those invocations and exposes Update & Shutdown and Update & Restart.

Written by the indexing model from the issue text.