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/infrastructure/test_subtitle_metadata_store.py

@@ -16,7 +16,7 @@ from __future__ import annotations
 
 from pathlib import Path
 
-from alfred.domain.subtitles.entities import SubtitleCandidate
+from alfred.domain.subtitles.entities import SubtitleScanResult
 from alfred.application.subtitles.placer import PlacedTrack
 from alfred.domain.subtitles.value_objects import (
     SubtitleFormat,
@@ -32,8 +32,8 @@ ENG = SubtitleLanguage(code="eng", tokens=["en"])
 
 def _track(
     lang=FRA, *, embedded: bool = False, confidence: float = 0.92
-) -> SubtitleCandidate:
-    return SubtitleCandidate(
+) -> SubtitleScanResult:
+    return SubtitleScanResult(
         language=lang,
         format=SRT,
         subtitle_type=SubtitleType.STANDARD,