test: 更新 model mapping 测试用例期望值

backend/internal/service/antigravity_model_mapping_test.go

@@ -131,7 +131,7 @@ func TestAntigravityGatewayService_GetMappedModel(t *testing.T) {
 			name:           "系统映射 - claude-sonnet-4-5-20250929",
 			requestedModel: "claude-sonnet-4-5-20250929",
 			accountMapping: nil,
-			expected:       "claude-sonnet-4-5-thinking",
+			expected:       "claude-sonnet-4-5",
 		},
 
 		// 3. Gemini 透传