Improve .desktop file generation for KDE Plasma (Categories and Visibility) #386

Hello,

I am a Bazzite (Fedora-based immutable) user, and I've noticed that WebApps created with WebApp Manager have some integration issues on KDE Plasma. To fix this, I developed a script, but the Bazzite maintainers suggested that these improvements should be implemented directly in the WebApp Manager (upstream).

The Issues:

When a WebApp is created, the generated .desktop file often lacks proper metadata for a seamless experience on KDE:

1. Visibility: WebApps sometimes default to or end up with NoDisplay=true, making them invisible in the application launcher.
2. Categories: The files often lack the Internet or Network categories, meaning they don't show up in the expected menu sections.
3. Taskbar Grouping: The StartupWMClass often causes the WebApp to be grouped under the main Chrome/Browser icon in the taskbar instead of having its own independent icon.

Proposed Solution:

I recommend that the .desktop file generation logic be updated to include/ensure the following entries:

• Categories: Add Network;WebBrowser;Internet;
• Visibility: Ensure NoDisplay=false
• Type: Ensure Type=Application
• Icon Fix: Avoid or correctly map StartupWMClass to prevent grouping with the main browser process.

Why this matters:

On immutable systems like Bazzite or SteamOS, users cannot easily modify system files. Having the WebApp Manager generate "correct" files from the start would greatly improve the out-of-the-box experience for the entire KDE community.

Thank you for your work on this great tool!