`intel-npu` engine fails with a large image

Nobody has claimed this yet.

With a larger image, the intel-npu engine fails, responding with:
```
{'error': 'Mediapipe execution failed. MP status - INVALID_ARGUMENT: CalculatorGraph::Run() failed: \nCalculator::Process() for node "LLMExecutor" failed: Request processing failed, check its correctness.'}
```

The server logs report the real reason:
```
VLM pipeline on NPU may only process input embeddings up to 1024 tokens. 1165 is passed.
Set the "MAX_PROMPT_LEN" config option to increase the limit.
```

Intel has mentioned this before:
> for VLMs on NPU it is easy to get a lot of input tokens so you may need to set MAX_PROMPT_LEN as described here for LLMs https://docs.openvino.ai/2025/openvino-workflow-generative/inference-with-genai/inference-with-genai-on-npu.html .

Increasing the maximum prompt length does not work, as ovms does not parse the option correctly. See [upstream bug report](https://github.com/openvinotoolkit/model_server/issues/3703).

Start with the reported intel-npu failure and the linked upstream model_server issue, then inspect how MAX_PROMPT_LEN is passed to the VLM pipeline. Confirm whether the upstream parsing problem is resolved and whether a large-image request can process more than 1024 tokens; the issue is done when this path works or its upstream dependency is clearly documented.

Written by the indexing model from the issue text.