Add endpoint to retrieve specific model info

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Hi
Introduces a new GET /v1/models/{model} endpoint to fetch details for a specific model
Updates ContentView to display this endpoint
Adds corresponding tests in test_server.py

why:

• Allows tools, after an app restart, to consult this endpoint to verify whether the previously selected model is still available.
• Supports tests that need to query a specific model, in a full tests suite about model