ENG-2755: Show capacity for prime rl models

[manveerxyz]

Note

Low Risk
Small, read-only CLI/API model change; primary risk is compatibility if the backend omits or renames the atCapacity field.

Overview
The RL models API/CLI output now exposes per-model capacity via a new RLModel.at_capacity field (mapped from atCapacity).

prime rl models table output is updated to include a Status column that renders models as Available vs At Capacity based on that flag (JSON output includes the new field via model_dump).

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