model : add H2O-Lightning-4B decision model (#30361)

* model : add H2O-Lightning-4B decision model

Adds the h2o-lightning decision type for h2oai/h2o-lightning-4b
(Qwen3.5-4B with a merged decision LoRA).

None of the existing types match this model. It answers with " A"
rather than "A", uses up to 255 labels, and was trained on Python
json.dumps text, so floats like 12.0 must render as 12.0.

The converter writes the decision metadata and the systemone template
from the model's serve_config.json and refuses a config that doesn't
match. Tests skip unless the tiny test model is available locally.

Assisted-by: Claude Opus 5.5

* rm redundant code

* put labels to gguf

---------

Co-authored-by: Jonathan C. McKinney <jon.mckinney@h2o.ai>
Co-authored-by: Xuan Son Nguyen <son@huggingface.co>

tools/server/server-common.cpp

@@ -215,6 +215,7 @@ std::vector<std::string> server_model_output_modalities(common_decision_type dec
         case COMMON_DECISION_TYPE_VLLM_D3:
         case COMMON_DECISION_TYPE_LFM2_D1:
         case COMMON_DECISION_TYPE_LFM2_D1_OMNI:
+        case COMMON_DECISION_TYPE_H2O_LIGHTNING:
             return {"decisions"};
         case COMMON_DECISION_TYPE_GRANITE_SWITCH:
             return {"text", "decisions"};