refactor(subtitles): rename SubtitleCandidate → SubtitleScanResult

The old name conflated 'might become a placed subtitle' with 'what a
scan pass produced'. The class is the output of a scan/identify pass —
language/format may still be None while classification is in progress,
confidence reflects classifier certainty, raw_tokens holds filename
fragments under analysis. SubtitleScanResult says that directly.

Pure rename + refreshed docstring; no behavior change. Touches the
domain entity, the matcher/identifier/utils services, the
manage_subtitles use case, the placer, the metadata store, the
shared-media cross-ref comment, and 7 test modules.

tests/application/test_manage_subtitles.py

@@ -40,7 +40,7 @@ from alfred.application.filesystem.manage_subtitles import (
     _to_imdb_id,
     _to_unresolved_dto,
 )
-from alfred.domain.subtitles.entities import MediaSubtitleMetadata, SubtitleCandidate
+from alfred.domain.subtitles.entities import MediaSubtitleMetadata, SubtitleScanResult
 from alfred.application.subtitles.placer import PlacedTrack, PlaceResult
 from alfred.domain.subtitles.value_objects import (
     ScanStrategy,
@@ -63,8 +63,8 @@ def _track(
     is_embedded: bool = False,
     raw_tokens: list[str] | None = None,
     file_size_kb: float | None = None,
-) -> SubtitleCandidate:
-    return SubtitleCandidate(
+) -> SubtitleScanResult:
+    return SubtitleScanResult(
         language=lang,
         format=fmt,
         subtitle_type=stype,