fix(core): fix lint/type issues and small refactors

ts/systemd.ts

@@ -174,7 +174,7 @@ WantedBy=multi-user.target
           }`,
         );
       }
-    } catch (_error) {
+    } catch (error) {
       // If version check fails, show at least the current version
       try {
         const nupst = this.daemon.getNupstSnmp().getNupst();