feat: restore Copilot preset and auth center tab in settings

Re-enable GitHub Copilot provider preset and the OAuth auth center tab
that were temporarily hidden due to abnormal consumption rates. The
Copilot optimizer introduced in the previous commit addresses the
underlying issue.

src/config/claudeProviderPresets.ts

@@ -707,7 +707,6 @@ export const providerPresets: ProviderPreset[] = [
     requiresOAuth: true,
     icon: "github",
     iconColor: "#000000",
-    hidden: true, // 临时隐藏：用户反馈消耗速度过快
   },
   {
     name: "Nvidia",