refactor(subtitles): RuleScope.level → RuleScopeLevel enum

Six niveaux possibles (global, release_group, movie, show, season,
episode) étaient passés en str libre, le commentaire docstring servant
de seule documentation. Introduit RuleScopeLevel(str, Enum) — toujours
sérialisable en YAML, mais le set fixe est désormais imposé par le
typage. to_dict() sort explicitement .value pour rester safe côté
écrivains YAML.

tests/domain/test_subtitle_utils.py

@@ -28,6 +28,7 @@ from alfred.domain.subtitles.entities import MediaSubtitleMetadata, SubtitleCand
 from alfred.domain.subtitles.services.utils import available_subtitles
 from alfred.domain.subtitles.value_objects import (
     RuleScope,
+    RuleScopeLevel,
     SubtitleFormat,
     SubtitleLanguage,
     SubtitleMatchingRules,
@@ -257,7 +258,7 @@ class TestSubtitleRuleSet:
     def test_override_partial_keeps_parent_for_unset_fields(self):
         parent = SubtitleRuleSet.global_default()
         child = SubtitleRuleSet(
-            scope=RuleScope(level="show", identifier="tt1"),
+            scope=RuleScope(level=RuleScopeLevel.SHOW, identifier="tt1"),
             parent=parent,
         )
         child.override(languages=["jpn"])
@@ -267,14 +268,14 @@ class TestSubtitleRuleSet:
         assert rules.min_confidence == parent.resolve(_DEFAULT_RULES).min_confidence
 
     def test_to_dict_only_emits_set_deltas(self):
-        rs = SubtitleRuleSet(scope=RuleScope(level="show", identifier="tt1"))
+        rs = SubtitleRuleSet(scope=RuleScope(level=RuleScopeLevel.SHOW, identifier="tt1"))
         rs.override(languages=["fra"])
         out = rs.to_dict()
         assert out["scope"] == {"level": "show", "identifier": "tt1"}
         assert out["override"] == {"languages": ["fra"]}
 
     def test_to_dict_full_override(self):
-        rs = SubtitleRuleSet(scope=RuleScope(level="global"))
+        rs = SubtitleRuleSet(scope=RuleScope(level=RuleScopeLevel.GLOBAL))
         rs.override(
             languages=["fra"],
             formats=["srt"],