Add Modal smoke training workflow

[zrr1999]

Summary

• add smoke-training controls to the existing training CLI via --num-epochs, --max-train-batches, and --eval-interval
• add a Modal app that can warm Hugging Face caches in a Volume and run a low-cost smoke training job with datasets/checkpoints mounted into the existing repo layout
• document the new local smoke-test path and Modal workflow in the README

Validation

• uv run ruff check src/
• uv run --with modal pyright src/recognize_modal/app.py

Notes

• the repository already has pre-existing broader pyright src/ failures outside this PR; this PR only validated the new Modal module directly and kept ruff green across src/