Fix todo retrieval ordering by position

[ded-furby]

Summary

• order get_all_todos() by the stored position column instead of relying on SQLite row order
• add a regression test that inserts rows out of order to prove the returned todo list follows position

Closes #5.

Validation

• python -m pytest tests/test_database.py -k ordered_by_position
• python -m pytest tests/test_database.py
• python -m trushell --help
• trushell --help

Notes

• python -m pytest on my local macOS environment still hits the pre-existing tests/test_sound.py::test_play_alarm_uses_quiet_subprocess platform assumption (afplay vs paplay).
• python -m ruff check . currently fails on the repository's existing pyproject.toml target-version = ["py310"] entry, which Ruff 0.15.15 does not parse as valid TOML.