Resolves#36024 and #34501.
Main change is about stop using the first user in the `users` command
output [*] and instead use `loginctl` commands to pick the correct
current active GUI user.
[*] `users` was returning empty on some new distributions, and in
multi-sessions we were always picking the first one (even if it wasn't
active).
- [X] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
## Testing
- [x] QA'd all new/changed functionality manually
## fleetd/orbit/Fleet Desktop
- [x] Verified compatibility with the latest released version of Fleet
(see [Must
rule](https://github.com/fleetdm/fleet/blob/main/docs/Contributing/workflows/fleetd-development-and-release-strategy.md))
- [x] If the change applies to only one platform, confirmed that
`runtime.GOOS` is used as needed to isolate changes
- [x] Verified that fleetd runs on macOS, Linux and Windows
- [x] Verified auto-update works from the released version of component
to the new version (see [tools/tuf/test](../tools/tuf/test/README.md))
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
## Release Notes
* **Bug Fixes**
* Fixed Fleet Desktop startup to correctly detect and use the active GUI
session on Linux systems.
* Improved GUI user detection for dialog prompts, ensuring system
dialogs run in the proper user context.
* **Improvements**
* Enhanced error reporting and logging clarity for GUI session detection
failures.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
