fix(relay): handle dead connections and preserve usage on refresh failure

Use received frames for peer liveness and reject new requests after terminal relay failures. Keep authoritative usage snapshots separate from refresh errors, bound request lifetime, and guard concurrent refreshes and runtime switches.

Add regression coverage for relay liveness, terminal rejections, quota failures, cancellation and request deadlines. Validated with 51 focused tests, workspace type-check and lint, web build and mobile assets.

packages/ui/src/components/sections/usage/UsageSidebar.tsx

@@ -98,7 +98,7 @@ export const UsageSidebar: React.FC<UsageSidebarProps> = ({ onItemSelect }) => {
           const percent = getUsagePercent(result?.usage);
           const tone = resolveUsageTone(percent);
           const isSelected = provider.id === selectedProviderId;
-          const configured = result?.configured ?? false;
+          const configured = result?.configured;
 
           const statusStyle = !configured
             ? { backgroundColor: 'var(--surface-muted-foreground)', opacity: 0.4 }
@@ -129,7 +129,7 @@ export const UsageSidebar: React.FC<UsageSidebarProps> = ({ onItemSelect }) => {
                 <span className="typography-ui-label font-normal truncate flex-1 min-w-0 text-foreground">
                   {provider.name}
                 </span>
-              {!configured && (
+              {configured === false && (
                 <span className="typography-micro text-muted-foreground/60 flex-shrink-0">{t('settings.usage.sidebar.status.notSet')}</span>
               )}
             </button>