Ollama: surface model tags/versions in `info()`

[himanshu231204]

Background

md.info() today does not expose the available tags/versions for a model (e.g. llama3:70b, llama3:latest).

Why it matters

Contributors and users need to pick a specific size/variant before installing.

Acceptance criteria

• Ollama adapter lists tags via the API and maps them to domain/model.py variants.
• md.info("llama3") includes a tags/variants section.
• Unit tests covering tag parsing.

Where to look

• src/modeldock/adapters/runtimes/ollama.py, src/modeldock/domain/model.py

How to claim

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