docs: clarify deterministic quick start requirements

[rustfuture]

State the Python requirement, use python3 explicitly and explain where the deterministic run writes its summary and report. Add Windows command/path guidance while keeping the first run free of optional model dependencies.

Validation

All listed checks completed locally with exit code 0. Run output paths used temporary directories to preserve committed evidence.

git diff --check
python3 -m rsi_framework --config config/default.json --output /var/folders/v1/5g8zpd5j0h56kyw4dn14f_g40000gn/T/portfolio-quickstart-c03_zqaj/rsi-run
python3 -m unittest discover -s tests
python3 -m rsi_framework.reporting --results results --readme README.md --check

Tested on macOS with Python 3.14.5; Windows and the optional model path were not run.