docs(cli): add Vercel provider to setup and doctor

src/cli/setup/providers.test.ts

@@ -61,4 +61,18 @@ describe('setupProviders', () => {
     expect(config.models.fast).toBeDefined();
     expect(config.models.fast.provider).toBe('anthropic');
   });
+
+  it('configures vercel gateway as default provider (second tier)', async () => {
+    // Pick "More providers..." then pick "Vercel AI Gateway".
+    // Prompts: api key, endpoint, model, then confirm fast tier.
+    const rl = mockReadline(['4', '3', 'sk-vercel-test123', '', '', 'n']);
+    const p = createPrompter(rl);
+    const builder = new ConfigBuilder();
+    await setupProviders(p, builder);
+    const config = builder.build();
+    expect(config.models.default.provider).toBe('vercel');
+    expect(config.models.default.api_key).toBe('sk-vercel-test123');
+    expect(config.models.default.endpoint).toBe('https://ai-gateway.vercel.sh/v1');
+    expect(config.models.default.model).toBe('openai/gpt-4.1');
+  });
 });