Fix notify

[ygerlach]

I have not tested this, as i didnt had time to setup fedora and reproduce the problem, but this should
Fix #474

(EDIT: I wasnt able to reproduce the initial issue, but my change helped some notifications to appear at all)

I branched from one of my other branches (#459) as i improved the handling of commands, that should not be run by root, what i needed here. So this branch shares some commits with #459 but they should not conflict and can be merged in any order (i will fix all conflicts otherwise)

The center of this fix is executing "notify-send" as user and not as root. But i also made the call async.

[Copilot]

Pull request overview

This PR fixes notification issues by ensuring notify-send executes as the actual user rather than root, and makes the notification call asynchronous. The fix addresses issue #474 where notifications weren't appearing.

Key changes:

• Introduces exec_user_async() to execute commands as the unprivileged user using pkexec
• Refactors user ID and username lookup functions to use POSIX APIs directly instead of shell commands
• Updates notification system to use the new async user execution method

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

File	Description
src/Utility/TeeJee.System.vala	Refactored user ID/username lookup to use POSIX APIs; changed get_user_id() to use SUDO_UID instead of SUDO_USER; simplified xdg_open() to use new exec_user_async()
src/Utility/TeeJee.Process.vala	Added new exec_user_async() function to execute commands as unprivileged user with pkexec wrapper when running with elevated privileges
src/Utility/OSDNotify.vala	Changed notification from synchronous exec_sync() to asynchronous exec_user_async() to run notify-send as the actual user
src/Gtk/MainWindow.vala	Connected AboutDialog's activate_link signal to xdg_open() to handle link clicks with user-level execution

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[mtwebster]

Btw, I'm not using copilot only, but it's another pair of 'eyes' and it's not terrible at finding stupid mistakes and occasionally interesting things.