Deleted workouts are marked with deleted_at instead of being removed.
All queries filter on deleted_at IS NULL. New update_workout() does
soft-delete + recreate preserving the original timestamp. PUT endpoint
at /api/workouts/{id}. POST /api/workouts now accepts a note field.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>