fix(cli): support file payload args for step and eval run

[jt-poolside]

Summary

• fix bridge run --results-file so file-provided results are used for actual step invocation
• add file payload args for step run:
  • --input-file
  • --results-file
• add file payload arg for eval run:
  • --context-file
• keep existing inline args and --context @path behavior for compatibility
• add explicit argument validation for mutually exclusive / missing payload sources
• add CLI tests covering step and eval file-argument paths

Why

Forge now supports sandbox file payload transport to avoid argv size limits; SDK CLI needs reliable file-arg support for the execution path.

Test Plan

• uv run pytest tests/test_cli.py tests/test_invoke_step.py tests/test_eval.py

Cross-repo

Companion Forge PR switches step/eval runtime payload transport to sandbox files with compatibility fallback.

[tkpoolside]

Let's update readme but otherwise LGTM!

[jt-poolside]

Let's update readme but otherwise LGTM!

good catch. done