Fix EndpointsApiTest OAuth credentials to use env vars

Use BW_CLIENT_ID and BW_CLIENT_SECRET from environment variables
instead of hardcoded fake credentials, matching the pattern used by
CallsApiTest and other unit tests. The OAuth token request hits the
real auth server before reaching Prism, so fake credentials cause
all 5 tests to fail with invalid_client errors.

Generated from Claude9 with Claude Code

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: smoghe-bw

src/test/java/com/bandwidth/sdk/unit/api/EndpointsApiTest.java

@@ -3,9 +3,7 @@
 import com.bandwidth.sdk.ApiClient;
 import com.bandwidth.sdk.ApiException;
 import com.bandwidth.sdk.ApiResponse;
-import com.bandwidth.sdk.Configuration;
 import com.bandwidth.sdk.api.EndpointsApi;
-import com.bandwidth.sdk.auth.HttpBasicAuth;
 import com.bandwidth.sdk.model.CreateEndpointResponse;
 import com.bandwidth.sdk.model.CreateEndpointResponseData;
 import com.bandwidth.sdk.model.CreateWebRtcConnectionRequest;
@@ -34,7 +32,7 @@
  */
 @SuppressWarnings("null")
 public class EndpointsApiTest {
-    private static ApiClient oauthClient = new ApiClient("test-client-id", "test-client-secret", null);
+    private static ApiClient oauthClient = new ApiClient(BW_CLIENT_ID, BW_CLIENT_SECRET, null);
     private static EndpointsApi api = new EndpointsApi(oauthClient);
 
     @BeforeAll