Fix: Display GitHub Copilot Student in UI and add model discovery

- Add 'github-copilot' to LlmProviderFlavor type in settings dialog
- Add GitHub Copilot Student to moreProviders array in UI
- Add github-copilot to initial providerConfigs state
- Add isGitHubCopilot flag to handle Device Flow auth flow
- Add GitHub Copilot authentication button in settings UI
- Add GitHub Copilot models (6 models) to listOnboardingModels() output
- Add eslint-disable comment for mock fetch in tests

This fixes the issue where GitHub Copilot Student was not appearing in the Models dropdown in the Settings dialog.

apps/x/packages/core/src/auth/github-copilot.test.ts

@@ -13,7 +13,7 @@ const originalFetch = global.fetch;
 const mockFetch = vi.fn();
 
 beforeEach(() => {
-  global.fetch = mockFetch as any;
+  global.fetch = mockFetch as any; // eslint-disable-line @typescript-eslint/no-explicit-any
 });
 
 afterEach(() => {

apps/x/packages/core/src/models/models-dev.ts

@@ -222,5 +222,19 @@ export async function listOnboardingModels(): Promise<{ providers: ProviderSumma
     });
   }
 
+  // Add GitHub Copilot models
+  providers.push({
+    id: "github-copilot",
+    name: "GitHub Copilot Student",
+    models: [
+      { id: "gpt-4o", name: "GPT-4o" },
+      { id: "gpt-4-turbo", name: "GPT-4 Turbo" },
+      { id: "gpt-4", name: "GPT-4" },
+      { id: "gpt-3.5-turbo", name: "GPT-3.5 Turbo" },
+      { id: "claude-3.5-sonnet", name: "Claude 3.5 Sonnet" },
+      { id: "claude-3-opus", name: "Claude 3 Opus" },
+    ],
+  });
+
   return { providers, lastUpdated: fetchedAt };
 }