fix: register missing updater commands

- Add check_app_updates, install_app_updates, get_update_channel, set_update_channel to Tauri handler
- Add unit tests for update channel functionality

This fixes the 'Command check_app_updates not found' and 'Failed to update channel' errors reported in the latest build.

src-tauri/src/commands/system.rs

@@ -626,4 +626,17 @@ mod updater_tests {
         assert!(!is_newer_version("", "1.0.0"));
         assert!(!is_newer_version("1.0.0", ""));
     }
+
+    #[test]
+    fn test_update_channel_default() {
+        let settings = AppSettings::default();
+        assert_eq!(settings.update_channel, "stable");
+    }
+
+    #[test]
+    fn test_update_channel_serialization() {
+        let settings = AppSettings::default();
+        let json = serde_json::to_string(&settings).unwrap();
+        assert!(json.contains("\"stable\""));
+    }
 }

src-tauri/src/lib.rs

@@ -256,6 +256,10 @@ pub fn run() {
             commands::system::get_sudo_config_status,
             commands::system::test_sudo_password,
             commands::system::clear_sudo_password,
+            commands::system::check_app_updates,
+            commands::system::install_app_updates,
+            commands::system::get_update_channel,
+            commands::system::set_update_channel,
             // MCP Servers
             mcp::commands::list_mcp_servers,
             mcp::commands::create_mcp_server,