Fix JS/TS lint issues in web frontend

- Remove unused imports (ES6UnusedImports): AboutDialog, Dashboard, SetupWizard,
  jobs.astro, login.astro, settings.astro, stats.astro
- Prefix unused variables with underscore (JSUnusedLocalSymbols): _previousTheme,
  _lastJob, _loading, _detailLoading, _page, _success/_setSuccess
- Remove unused cn/clsx/twMerge from SystemStatus.tsx
- Add await to async calls (ES6MissingAwait) in JobManager, NotificationSettings,
  ScheduleSettings, SetupWizard, WatchFolders
- Add void keyword for ignored promises (JSIgnoredPromiseFromCall) in useEffect
  callbacks across Dashboard, FileSettings, HardwareSettings, JobManager, LogViewer,
  NotificationSettings, ResourceMonitor, ScheduleSettings, SetupWizard, StatsCharts,
  SystemSettings, SystemStatus, TranscodeSettings, WatchFolders
- CSS: Remove redundant background-color overridden by background shorthand;
  remove unused .btn selector
- HTML: Associate labels with form inputs via for/id attributes in login.astro

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

web/src/components/NotificationSettings.tsx

@@ -26,7 +26,7 @@ export default function NotificationSettings() {
     const [newEvents, setNewEvents] = useState<string[]>(["completed", "failed"]);
 
     useEffect(() => {
-        fetchTargets();
+        void fetchTargets();
     }, []);
 
     const fetchTargets = async () => {
@@ -63,7 +63,7 @@ export default function NotificationSettings() {
                 setNewName("");
                 setNewUrl("");
                 setNewToken("");
-                fetchTargets();
+                await fetchTargets();
             }
         } catch (e) {
             console.error(e);
@@ -74,7 +74,7 @@ export default function NotificationSettings() {
         if (!confirm("Remove this notification target?")) return;
         try {
             await apiFetch(`/api/settings/notifications/${id}`, { method: "DELETE" });
-            fetchTargets();
+            await fetchTargets();
         } catch (e) {
             console.error(e);
         }