Empty placeholder, all four status pill branches (QUEUED/DONE/FAILED/
RUNNING), error-detail disclosure on FAILED, Personalisiert vs Basis
type label, COLLAPSED_COUNT visible runs, person columns visibility
toggle, em-dash CER fallback.
11 tests covering ~25 of TrainingHistory's branches.
Refs #496.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
