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>

src/llama-model.cpp

@@ -1549,6 +1549,9 @@ void llama_model_base::load_hparams(llama_model_loader & ml) {
         hparams.n_cls_out = classifier_labels.size();
     }
 
+    // for decision models
+    ml.get_arr(LLM_KV_DECISION_LABELS, decision_labels, false);
+
     // per-arch hparams
     load_arch_hparams(ml);
 
@@ -3438,6 +3441,14 @@ const char * llama_model_cls_label(const struct llama_model * model, uint32_t i)
     return nullptr;
 }
 
+const char * llama_model_decision_label(const struct llama_model * model, uint32_t i) {
+    if (i < model->decision_labels.size()) {
+        return model->decision_labels[i].c_str();
+    }
+
+    return nullptr;
+}
+
 // deprecated
 int32_t llama_n_ctx_train(const llama_model * model) {
     return llama_model_n_ctx_train(model);