fix: remove dead localStorage writes and hardcoded key

- Remove unused `dns_settings_enabled` localStorage writes in
  setting-clash.tsx — state is sourced from verge config, these
  writes were never read anywhere.
- Replace hardcoded `'last_check_update'` localStorage read in
  system-info-card.tsx with exported `readLastCheckTime()` from
  the useUpdate hook, keeping the key in a single source of truth.

src/components/setting/setting-clash.tsx

@@ -78,7 +78,6 @@ const SettingClash = ({ onError }: Props) => {
   const handleDnsToggle = useLockFn(async (enable: boolean) => {
     try {
       setDnsSettingsEnabled(enable)
-      localStorage.setItem('dns_settings_enabled', String(enable))
       await patchVerge({ enable_dns_settings: enable })
       await invoke('apply_dns_config', { apply: enable })
       setTimeout(() => {
@@ -86,7 +85,6 @@ const SettingClash = ({ onError }: Props) => {
       }, 500)
     } catch (err: any) {
       setDnsSettingsEnabled(!enable)
-      localStorage.setItem('dns_settings_enabled', String(!enable))
       showNotice.error(err)
       await patchVerge({ enable_dns_settings: !enable }).catch(() => {})
       throw err