Rethink worker tasks & dependencies

Maybe it makes sense to make the dependencies more granular. E.g. the alignment could start aligning to the already transcribed bars (maybe with some safety distance) even if not the whole document is transcribed yet.
This could also lead to some cool UX, where we really display one worker for each task (similiar to normal users) and each worker can report their own status

Start by tracing how worker tasks, dependencies, alignment, and transcription progress currently interact; no files or tests are named in the issue. Define the scope with maintainers before coding, including granular dependencies, partial alignment, and per-worker status display; done requires an agreed design and implementation plan.

Written by the indexing model from the issue text.