fix: Update Channel setting not persisting after save

The Update Channel dropdown reverted to "stable" after saving because the
frontend was overwriting the user's saved preference with the running
version's channel. Now the saved setting takes priority over the detected
channel.

Related to #738

frontend-modern/src/components/Settings/Settings.tsx

@@ -2040,7 +2040,9 @@ const Settings: Component<SettingsProps> = (props) => {
         setVersionInfo(version);
         // Also set it in the store so it's available globally
         updateStore.checkForUpdates(); // This will load version info too
-        if (version.channel) {
+        // Only use version.channel as fallback if user hasn't configured a preference
+        // The user's saved updateChannel preference should take priority
+        if (version.channel && !systemSettings.updateChannel) {
           setUpdateChannel(version.channel as 'stable' | 'rc');
         }
       } catch (error) {