Add fitness workout recommender domain

[Cosmhyccc]

Summary

• add a distinct fitness/workout domain for the AO Labs paid bounty in [OPEN Bounty] - Apply our Recommender to a new domain/dataset ao_pyth#9
• include a local workout catalog, deterministic binary encoding of workout metadata plus user context, and fallback ranking for reviewers without private AO packages
• add a Streamlit demo that can use an AO Agent when ao_core/ao_arch are installed, while still running in fallback mode otherwise
• document how to run the demo and tests

Validation

• python3 -m unittest discover -s tests
• python3 -m py_compile fitness_domain.py fitness_recommender.py arch__FitnessRecommender.py tests/test_fitness_domain.py
• git diff --check

Notes

This is intentionally separate from the existing YouTube app and from the current movie/music/recipe/learning/book bounty submissions, so it can be reviewed as an independent domain adaptation.