The placer performs filesystem I/O (os.link) — it belongs in the
application layer, not the domain. Domain services should be pure.
- Move alfred/domain/subtitles/services/placer.py to
alfred/application/subtitles/placer.py
- Move tests/domain/test_subtitle_placer.py to
tests/application/test_subtitle_placer.py
- Update all callers (manage_subtitles use case, metadata store, tests)
- Drop placer re-exports from domain.subtitles.services.__init__
