mtmd, model: allow skip build_vit() (#24077)

* add model

* nits

gguf-py/gguf/tensor_mapping.py

@@ -1426,6 +1426,7 @@ class TensorNameMap:
             "model.vision_tower.patch_embedder.input_proj", # gemma4
             "vision_tower.patch_embed.patchifier.proj", # dots.ocr
             "vision_model.conv1", # Step3-VL
+            "model.vision_embedder.patch_dense", # gemma4 unified
         ),
 
         MODEL_TENSOR.V_ENC_EMBD_NORM: (
@@ -1433,6 +1434,10 @@ class TensorNameMap:
             "vision_tower.patch_embed.patchifier.norm", # dots.ocr
         ),
 
+        MODEL_TENSOR.V_ENC_EMBD_PATCH_NORM: (
+            "model.vision_embedder.patch_ln{bid}", # gemma4 unified
+        ),
+
         MODEL_TENSOR.V_ENC_EMBD_POS: (
             "vision_tower.vision_model.embeddings.position_embedding",
             "model.vision_tower.embeddings.position_embedding", # minicpmv4_6
@@ -1448,6 +1453,7 @@ class TensorNameMap:
             "vision_model.radio_model.model.patch_generator.pos_embed", # Nemotron Nano v2 VL
             "model.vision_tower.patch_embedder.position_embedding_table", # gemma4
             "vision_model.positional_embedding", # Step3-VL
+            "model.vision_embedder.pos_embedding", # gemma4 unified
         ),
 
         MODEL_TENSOR.V_ENC_EMBD_IMGNL: (