feat: auto remove ollama local models if they are no longer there

[sharkymark]

I've manually removed some ollama-downloaded models with ollama rm <model name>

But in AI Toolkit, the local models are still there in the list and I have to manually remove them, one by one.

[microsoft-github-policy-service]

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[swatDong]

Thanks for the suggestion. Marked this as feature enhancement and will be tracked in further planning.