Drop ZHANLU_MODELS and ZHANLU_DEFAULT_MODEL config

Model list is always fetched live from the gateway model-info endpoint, so the
static fallback list was dead config with stale IDs (GLM-4.7 vs zhanlu/glm-4.7).
Default to zhanlu/auto when the request omits model.

internal/server/server_test.go

@@ -70,8 +70,6 @@ func setupTestServer(t *testing.T) (*httptest.Server, *httptest.Server, string)
 		PublicKeyPEM:       defaultTestPublicKey,
 		PhonePublicKeyPEM:  defaultTestPublicKey,
 		SM2PrivateKey:      testSM2Key,
-		Models:             []string{"GLM-4.7", "MiniMaxAI/MiniMax-M2.5"},
-		DefaultModel:       "GLM-4.7",
 		PluginVersion:      "1.4.2",
 	}
 	h := New(cfg)