fix(cli): isolate modelConfigUtils tests from system env vars

Use a clean process.env object instead of shallow-copying the original
environment. This prevents test failures when system has auth-related
env vars (e.g., OPENAI_API_KEY) that would interfere with test assertions.

packages/cli/src/utils/modelConfigUtils.test.ts

@@ -31,7 +31,8 @@ describe('modelConfigUtils', () => {
 
     beforeEach(() => {
       vi.resetModules();
-      process.env = { ...originalEnv };
+      // Start with a clean env - getAuthTypeFromEnv only checks auth-related vars
+      process.env = {};
     });
 
     afterEach(() => {