Load env files through Modal secrets

[ofekby]

Summary

• replace YAML env with env_file and reject old env config
• parse dotenv files locally and attach values to the Modal Worker via modal.Secret.from_dict
• fingerprint parsed env values deterministically by sorted key, ignoring comments/order/blank lines
• exclude configured env files from direct sync, including repo symlink paths
• bump version to 0.7.0 and update docs/playbooks

Verification

• uv run pytest -q
• uv run ruff check .
• uv run ty check
• uv build