Migration 017 set down_revision to "016_add_signal_context_snapshots",
but migration 016's revision id is "016", so `alembic upgrade head` could
not resolve the chain and the deploy's auto-alembic step would fail. Point
017 at the real id "016".
Add migration 018 to delete any persisted `paper_exit_mode` row. The July
2026 promotion changed the paper-trade exit default to `atr_trailing`, but
`get_exit_policy` reads a stored value before the code default, so an
environment that had ever saved the old `time` mode would silently keep it
and never run the promoted 3x ATR trailing exit. Mirrors migration 015's
one-way settings reset.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>