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/domain/test_subtitle_identifier.py

@@ -23,7 +23,7 @@ from unittest.mock import patch
 import pytest
 
 from alfred.domain.shared.ports import FileEntry
-from alfred.domain.subtitles.entities import SubtitleCandidate
+from alfred.domain.subtitles.entities import SubtitleScanResult
 from alfred.domain.subtitles.services.identifier import (
     SubtitleIdentifier,
     _count_entries,
@@ -310,8 +310,8 @@ class TestSizeDisambiguation:
             detection=TypeDetectionMethod.SIZE_AND_COUNT,
         )
 
-    def _track(self, lang_code: str, entries: int) -> SubtitleCandidate:
-        return SubtitleCandidate(
+    def _track(self, lang_code: str, entries: int) -> SubtitleScanResult:
+        return SubtitleScanResult(
             language=SubtitleLanguage(code=lang_code, tokens=[lang_code]),
             format=None,
             subtitle_type=SubtitleType.UNKNOWN,