Adds BlockController (block groups + blocks CRUD, items GET, full replace,
non-persisting preview) mirroring ScheduleController, plus four scheduling
search picker endpoints on SearchController (collections, television shows,
television seasons, smart collections). Response DTOs in ErsatzTV.Core/Api/
Scheduling; request DTOs with ToCommand index auto-assignment.
#144 S1 (#162)
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
