[client] Remove lazy connection UI toggle (#6661)

Lazy connections are now opt-out and controlled centrally by NB_LAZY_CONN,
MDM policy (lazyConnection), and the management feature flag (#6617). The
per-device UI toggle no longer fits this model: after #6617 the daemon stopped
persisting the setting and dropped it from GetConfig, so the Wails toggle always
read back OFF and its writes did not survive a restart.

Remove the toggle and the orphaned runtime plumbing, matching what main did for
the Fyne UI:
- drop the toggle from SettingsNetwork and the lazy i18n keys
- drop LazyConnectionEnabled from the UI settings service and SetConfig request
- drop the runtime-apply block in server.SetConfig
- delete Engine.SetLazyConnEnabled and ConnMgr.SetLocalLazyConn

The proto fields and FullStatus status reporting are left intact.

client/ui/frontend/src/modules/settings/SettingsNetwork.tsx

@@ -12,12 +12,6 @@ export function SettingsNetwork() {
     return (
         <>
             <SectionGroup title={t("settings.network.section.connectivity")}>
-                <FancyToggleSwitch
-                    value={config.lazyConnectionEnabled}
-                    onChange={(v) => setField("lazyConnectionEnabled", v)}
-                    label={t("settings.network.lazy.label")}
-                    helpText={t("settings.network.lazy.help")}
-                />
                 <FancyToggleSwitch
                     value={config.networkMonitor}
                     onChange={(v) => setField("networkMonitor", v)}