fix(providers): prevent stale models during refresh

Provider settings sheets can remain mounted while hidden, so the old display cache could survive into a different provider. Scope the cache to the active provider identity and remount the sheet when that identity changes.

packages/app/src/components/provider-settings-host.tsx

@@ -18,6 +18,7 @@ export function ProviderSettingsHost() {
 
   return (
     <ProviderDiagnosticSheet
+      key={`${serverId}:${provider}`}
       provider={provider}
       serverId={serverId}
       visible={visible}