server: support image+text input for embeddings (Qwen3-VL-Embedding)

[ngxson]

Target support: https://huggingface.co/Qwen/Qwen3-VL-Embedding-2B

Important

the original Qwen3-VL-Embedding model is missing 1_Pooling, I don't think it's actually ready to be used unless Qwen team fixed it (I already reached out to them, but got no responses)

But currently, the model is missing 1_Pooling, so it cannot be correctly converted to GGUF

This PR aims to support mixed text+image (and maybe audio input for models supporting it) using OAI-compat content-like schema:

{
    "input": [
        {
            "type": "text",
            "text": "mixed text and image input"
        },
        {
            "type": "image",
            "image_url": {
                "url": "https://huggingface.co/ggml-org/tinygemma3-GGUF/resolve/main/test/11_truck.png"
            }
        }
    ]
}

[ggerganov]

When you convert the model, try to add --sentence-transformers-dense-modules:

llama.cpp/convert_hf_to_gguf.py

Lines 10974 to 10981 in 294b2b4

	parser.add_argument(
	"--sentence-transformers-dense-modules", action="store_true",
	help=("Whether to include sentence-transformers dense modules."
	"It can be used for sentence-transformers models, like google/embeddinggemma-300m"
	"Default these modules are not included.")
	)

[CISC]

IIRC they forgot to add 1_Pooling initially on other embedding models too, since this one is not public yet maybe ask about it?

[ngxson]

Oh sorry I didn't notice that it's private 😅 temporary closing this to keep it under the radar

[Tokimorphling]

I've fixed the Qwen3-VL-Embedding issues in llama.cpp and verified the fix with regression tests. Check out the code here: https://github.com/Tokimorphling/qwen3-vl-embedding

The implementation of the Qwen3-VL series in llama.cpp seems to be problematic.