Update finetuning HTTP point and detect settings

[EthanReid]

Summary

• update the finetuning HTTP API reference so point and detect use max_objects instead of max_tokens
• document that query still uses max_tokens
• note that point and detect derive their output token budget from max_objects

Verification

• git -C /tmp/md-docs_http diff --check
• manual accuracy pass against the current Tuna API behavior for query, point, and detect request settings

[Copilot]

Pull request overview

Updates the finetuning HTTP API reference to reflect current Tuna behavior, especially around max_objects vs max_tokens, and expands documentation for rollouts/training.

Changes:

• Update point/detect settings to use max_objects (and clarify max_tokens is query-only).
• Expand /rollouts response documentation with additional rollout/training fields.
• Update /train_step docs to cover RL vs SFT groups, and add checkpoint download endpoint docs.

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