feat: implement transcode settings repository and integrate with local-files provider

k-tv-backend/domain/src/repositories.rs

@@ -111,3 +111,12 @@ pub trait ActivityLogRepository: Send + Sync {
     ) -> DomainResult<()>;
     async fn recent(&self, limit: u32) -> DomainResult<Vec<ActivityEvent>>;
 }
+
+/// Repository port for transcode settings persistence.
+#[async_trait]
+pub trait TranscodeSettingsRepository: Send + Sync {
+    /// Load the persisted cleanup TTL. Returns None if no row exists yet.
+    async fn load_cleanup_ttl(&self) -> DomainResult<Option<u32>>;
+    /// Persist the cleanup TTL (upsert — always row id=1).
+    async fn save_cleanup_ttl(&self, hours: u32) -> DomainResult<()>;
+}