OpenWebUI demo changes

[przepeck]

🛠 Summary

CVS-175208
Adding windows commands for demo, using OV models instead of external, changes in agentic usecase.
[Preview]https://openvino-doc.iotg.sclab.intel.com/preview/model-server/ovms_demos_integration_with_open_webui.html

🧪 Checklist

• Unit tests added.
• The documentation updated.
• Change follows security best practices.
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[Copilot]

Pull Request Overview

This PR updates the OpenWebUI integration demo to add Windows support, replace external models with pre-converted OpenVINO models, and update the agentic use case. The changes streamline the setup process by using the --pull parameter to download models directly instead of requiring manual export steps, and provide platform-specific instructions for both Windows and Linux environments.

Key changes:

• Added Windows-specific command examples alongside Linux/Docker commands using tab-set formatting
• Replaced external models (meta-llama, sentence-transformers, BAAI, dreamlike-art, OpenGVLab) with pre-converted OpenVINO models (Godreign, OpenVINO org models)
• Updated agentic use case from time server to weather server using MCP tools

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