feat(failover): add auto-failover master switch with proxy integration (#427)

* feat(failover): add auto-failover master switch with proxy integration

- Add persistent auto_failover_enabled setting in database
- Add get/set_auto_failover_enabled commands
- Provider router respects master switch state
- Proxy shutdown automatically disables failover
- Enabling failover auto-starts proxy server
- Optimistic updates for failover queue toggle

* feat(proxy): persist proxy takeover state across app restarts

- Add proxy_takeover_{app_type} settings for per-app state tracking
- Restore proxy takeover state automatically on app startup
- Preserve state on normal exit, clear on manual stop
- Add stop_with_restore_keep_state method for graceful shutdown

* fix(proxy): set takeover state for all apps in start_with_takeover

src/components/usage/UsageDashboard.tsx

@@ -26,9 +26,7 @@ export function UsageDashboard() {
       <div className="flex flex-col sm:flex-row sm:items-center justify-between gap-4">
         <div className="flex flex-col gap-1">
           <h2 className="text-2xl font-bold">{t("usage.title")}</h2>
-          <p className="text-sm text-muted-foreground">
-            {t("usage.subtitle")}
-          </p>
+          <p className="text-sm text-muted-foreground">{t("usage.subtitle")}</p>
         </div>
 
         <Tabs