Feature/workout builder enhancements (#65)

* Add Time Under Tension Beast mode across builder + workout-time, keep UI label consistent

* Workout builder enhancements: past-date scheduling, progression options, UI polish, and tests

* Restore progression settings when loading builder plans

* adding back in progression

* adding back in progression

* Restore progression settings when loading builder plans

* Handle legacy builder snapshots without progression columns

---------

Co-authored-by: Codex Agent <codex-agent@example.com>

Author: exerciselibrary