Point the legacy desktop app options at the published package

The GTK3 build shipped under its own netbird-ui-gtk3 name with
Conflicts/Replaces on netbird-ui, so it coexists with the current build in
the regular repository. The separate repository paths the previous commit
assumed were never created: dists/gtk3 and yum-gtk3/$basearch both 404, and
the yum repository is flat rather than per-basearch. Drop them and install
netbird-ui-gtk3 from the regular repository instead.

Verified in Docker that the rendered commands install netbird 0.77.0 and
netbird-ui-gtk3 0.77.0 on Ubuntu 22.04 and Debian 12.

Remove the RHEL 9 option: the RPM requires webkit2gtk4.1 (or
libwebkit2gtk-4_1-0), but RHEL 9 only ships webkit2gtk3, which provides the
4.0 API, and EPEL does not carry 4.1 either, so dnf cannot resolve it. The
general RHEL entry already directs version 9 users to the CLI.

The desktop app is published for x86_64 only, which the install step already
notes for every distribution that offers it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/modules/setup-netbird-modal/LinuxTab.tsx

@@ -74,6 +74,29 @@ const DISTROS: Distro[] = [
     ],
     note: "The desktop app needs Ubuntu 24.04 or Debian 13 and newer. On earlier releases install the CLI only.",
   },
+  {
+    // Legacy GTK3 / WebKit2GTK 4.1 build of the desktop app, for releases
+    // without WebKitGTK 6.0. It ships under its own netbird-ui-gtk3 name and
+    // conflicts with netbird-ui, so it lives in the regular repository.
+    label: "Ubuntu 22.04 / Debian 12 (APT)",
+    value: "apt-gtk3",
+    repository: [
+      "sudo apt-get update",
+      "sudo apt-get install ca-certificates curl gnupg -y",
+      "curl -sSL https://pkgs.netbird.io/debian/public.key | sudo gpg --dearmor --output /usr/share/keyrings/netbird-archive-keyring.gpg",
+      `echo 'deb [signed-by=/usr/share/keyrings/netbird-archive-keyring.gpg] https://pkgs.netbird.io/debian stable main' | sudo tee /etc/apt/sources.list.d/netbird.list`,
+      // On Ubuntu, libwebkit2gtk-4.1-0 comes from the universe component. It is
+      // enabled on stock images but can be switched off. Guarded by the ID
+      // check: `universe` is an Ubuntu-only shortcut that Debian rejects.
+      `if . /etc/os-release && [ "$ID" = ubuntu ]; then sudo apt-get install software-properties-common -y && sudo add-apt-repository -y universe; fi`,
+    ],
+    beforeInstall: ["sudo apt-get update"],
+    cli: "sudo apt-get install netbird",
+    // The package declares its libgtk-3-0, libwebkit2gtk-4.1-0 and xdg-utils
+    // dependencies, so apt pulls those in on its own.
+    desktopApp: ["sudo apt-get install netbird-ui-gtk3"],
+    note: "For releases without WebKitGTK 6.0, which get a GTK3 build of the desktop app. On Ubuntu it needs the universe component, which the repository step enables. On Ubuntu 24.04 or Debian 13 and newer use the Debian / Ubuntu (APT) option instead.",
+  },
   {
     label: "Fedora (DNF)",
     value: "fedora",